Switzerland's Stan Wawrinka signs autographs as he leaves after Russia's Dmitry Tursunov retired from their first round match due to an injury at the Australian Open tennis tournament at Melbourne Park, Australia, January 19, 2016. REUTERS/Jason Reed 

Switzerland's Stan Wawrinka signs autographs as he leaves after Russia's Dmitry Tursunov retired from their first round match due to an injury at the Australian Open tennis tournament at Melbourne Park, Australia, January 19, 2016. REUTERS/Jason Reed 

Russia's Dmitry Tursunov (R) shakes hands with Switzerland's Stan Wawrinka after Tursunov retired from their first round match due to an injury at the Australian Open tennis tournament at Melbourne Park, Australia, January 19, 2016. REUTERS/Jason Reed 

Russia's Dmitry Tursunov (R) shakes hands with Switzerland's Stan Wawrinka after Tursunov retired from their first round match due to an injury at the Australian Open tennis tournament at Melbourne Park, Australia, January 19, 2016. REUTERS/Jason Reed 

Russia's Dmitry Tursunov speaks to a trainer as he receives treatment during his first round match against Switzerland's Stan Wawrinka at the Australian Open tennis tournament at Melbourne Park, Australia, January 19, 2016. REUTERS/Jason Reed 

Russia's Dmitry Tursunov receives treatment during his first round match against Switzerland's Stan Wawrinka at the Australian Open tennis tournament at Melbourne Park, Australia, January 19, 2016. REUTERS/Jason Reed 

Nasser Al-Khelaifi (bottom R), President of Paris Saint-Germain soccer club, watches a men's singles match between Roger Federer of Switzerland and Dmitry Tursunov of Russia at the French Open tennis tournament at the Roland Garros stadium in Paris May 30, 2014. REUTERS/Gonzalo Fuentes (FRANCE - Tags: SPORT TENNIS)

Roger Federer of Switzerland wipes his face with a towel during his men's singles match against Dmitry Tursunov of Russia at the French Open tennis tournament at the Roland Garros stadium in Paris May 30, 2014. REUTERS/Gonzalo Fuentes (FRANCE - Tags: SPORT TENNIS)

Roger Federer of Switzerland returns a forehand to Dmitry Tursunov of Russia during their men's singles match at the French Open tennis tournament at the Roland Garros stadium in Paris May 30, 2014. REUTERS/Gonzalo Fuentes (FRANCE - Tags: SPORT TENNIS)

Roger Federer of Switzerland returns a backhand to Dmitry Tursunov of Russia during their men's singles match at the French Open tennis tournament at the Roland Garros stadium in Paris May 30, 2014. REUTERS/Gonzalo Fuentes (FRANCE - Tags: SPORT TENNIS)

Roger Federer of Switzerland acknowledges spectators after winning his men's singles match against Dmitry Tursunov of Russia at the French Open tennis tournament at the Roland Garros stadium in Paris May 30, 2014. REUTERS/Gonzalo Fuentes (FRANCE - Tags: SPORT TENNIS)

Roger Federer of Switzerland acknowledges spectators after winning his men's singles match against Dmitry Tursunov of Russia at the French Open tennis tournament at the Roland Garros stadium in Paris May 30, 2014. REUTERS/Gonzalo Fuentes (FRANCE - Tags: SPORT TENNIS)

Roger Federer of Switzerland eyes the ball during his men's singles match against Dmitry Tursunov of Russia at the French Open tennis tournament at the Roland Garros stadium in Paris May 30, 2014. REUTERS/Gonzalo Fuentes (FRANCE - Tags: SPORT TENNIS)

Roger Federer of Switzerland reaches out to return a backhand to Dmitry Tursunov of Russia during their men's singles match at the French Open tennis tournament at the Roland Garros stadium in Paris May 30, 2014. REUTERS/Stephane Mahe (FRANCE - Tags: SPORT TENNIS)

Roger Federer of Switzerland reaches out to return a forehand to Dmitry Tursunov of Russia during their men's singles match at the French Open tennis tournament at the Roland Garros stadium in Paris May 30, 2014. REUTERS/Stephane Mahe (FRANCE - Tags: SPORT TENNIS)

Roger Federer of Switzerland returns a backhand to Dmitry Tursunov of Russia during their men's singles match at the French Open tennis tournament at the Roland Garros stadium in Paris May 30, 2014. REUTERS/Stephane Mahe (FRANCE - Tags: SPORT TENNIS)

Roger Federer of Switzerland hits a return to Dmitry Tursunov of Russia during their men's singles match at the French Open tennis tournament at the Roland Garros stadium in Paris May 30, 2014. REUTERS/Stephane Mahe (FRANCE - Tags: SPORT TENNIS)

Roger Federer of Switzerland reaches out to return a backhand to Dmitry Tursunov of Russia during their men's singles match at the French Open tennis tournament at the Roland Garros stadium in Paris May 30, 2014. REUTERS/Stephane Mahe (FRANCE - Tags: SPORT TENNIS TPX IMAGES OF THE DAY)

Dmitry Tursunov of Russia returns a backhand to Roger Federer of Switzerland during their men's singles match at the French Open tennis tournament at the Roland Garros stadium in Paris May 30, 2014. REUTERS/Stephane Mahe (FRANCE - Tags: SPORT TENNIS)

Dmitry Tursunov of Russia competes in his men's singles match against Roger Federer of Switzerland at the French Open tennis tournament at the Roland Garros stadium in Paris May 30, 2014. REUTERS/Gonzalo Fuentes (FRANCE - Tags: SPORT TENNIS)

Mirka Federer (C), wife of Roger Federer of Switzerland, watches her husband competing in a men's singles match against Dmitry Tursunov of Russia at the French Open tennis tournament at the Roland Garros stadium in Paris May 30, 2014. REUTERS/Gonzalo Fuentes (FRANCE - Tags: SPORT TENNIS)

Roger Federer of Switzerland prepares to serve the ball to Dmitry Tursunov of Russia during their men's singles match at the French Open tennis tournament at the Roland Garros stadium in Paris May 30, 2014. REUTERS/Gonzalo Fuentes (FRANCE - Tags: SPORT TENNIS)

Roger Federer of Switzerland returns a backhand to Dmitry Tursunov of Russia during their men's singles match at the French Open tennis tournament at the Roland Garros stadium in Paris May 30, 2014. REUTERS/Stephane Mahe (FRANCE - Tags: SPORT TENNIS)

A close up shows the head band of Roger Federer of Switzerland from behind during his men's singles match against Dmitry Tursunov of Russia at the French Open tennis tournament at the Roland Garros stadium in Paris May 30, 2014. REUTERS/Stephane Mahe (FRANCE - Tags: SPORT TENNIS) 

Dmitry Tursunov of Russia returns a backhand to Roger Federer of Switzerland during their men's singles match at the French Open tennis tournament at the Roland Garros stadium in Paris May 30, 2014. REUTERS/Stephane Mahe (FRANCE - Tags: SPORT TENNIS)

Roger Federer of Switzerland eyes the ball during his men's singles match against Dmitry Tursunov of Russia at the French Open tennis tournament at the Roland Garros stadium in Paris May 30, 2014. REUTERS/Stephane Mahe (FRANCE - Tags: SPORT TENNIS)

Roger Federer of Switzerland returns a forehand to Dmitry Tursunov of Russia during their men's singles match at the French Open tennis tournament at the Roland Garros stadium in Paris May 30, 2014. REUTERS/Gonzalo Fuentes (FRANCE - Tags: SPORT TENNIS)

Roger Federer of Switzerland returns a backhand to Dmitry Tursunov of Russia during their men's singles match at the French Open tennis tournament at the Roland Garros stadium in Paris May 30, 2014. REUTERS/Gonzalo Fuentes (FRANCE - Tags: SPORT TENNIS)

Dmitry Tursunov of Russia competes in his men's singles match against Roger Federer of Switzerland at the French Open tennis tournament at the Roland Garros stadium in Paris May 30, 2014. REUTERS/Gonzalo Fuentes (FRANCE - Tags: SPORT TENNIS)

Roger Federer of Switzerland prepares to serve the ball to Dmitry Tursunov of Russia during their men's singles match at the French Open tennis tournament at the Roland Garros stadium in Paris May 30, 2014. REUTERS/Gonzalo Fuentes (FRANCE - Tags: SPORT TENNIS)

Dmitry Tursunov of Russia competes in his men's singles match against Roger Federer of Switzerland at the French Open tennis tournament at the Roland Garros stadium in Paris May 30, 2014. REUTERS/Gonzalo Fuentes (FRANCE - Tags: SPORT TENNIS)

Roger Federer of Switzerland reaches out to retrurn a backhand to Dmitry Tursunov of Russia during their men's singles match at the French Open tennis tournament at the Roland Garros stadium in Paris May 30, 2014. REUTERS/Gonzalo Fuentes (FRANCE - Tags: SPORT TENNIS)

Tomas Berdych of the Czech Republic returns the ball to Dmitry Tursunov of Russia during the Monte Carlo Masters in Monaco April 15, 2014. REUTERS/Eric Gaillard (MONACO - Tags: SPORT TENNIS) 

Tomas Berdych of the Czech Republic returns the ball to Dmitry Tursunov of Russia during the Monte Carlo Masters in Monaco April 15, 2014. REUTERS/Eric Gaillard (MONACO - Tags: SPORT TENNIS) 

Tomas Berdych of the Czech Republic returns the ball to Dmitry Tursunov of Russia during the Monte Carlo Masters in Monaco April 15, 2014. REUTERS/Eric Gaillard (MONACO - Tags: SPORT TENNIS) 

Tomas Berdych of the Czech Republic returns the ball to Dmitry Tursunov of Russia during the Monte Carlo Masters in Monaco April 15, 2014. REUTERS/Eric Gaillard (MONACO - Tags: SPORT TENNIS) 

Dmitry Tursunov of Russia hits a return to Lukas Lacko of Slovakia during their men's singles match at the ATP Dubai Tennis Championships, February 24, 2014. REUTERS/Saleh Salem (UNITED ARAB EMIRATES - Tags: SPORT TENNIS) 

Dmitry Tursunov of Russia returns the ball to Lukas Lacko of Slovakia during their men's singles match at the ATP Dubai Tennis Championships, February 24, 2014. REUTERS/Faisal Al Nasser (UNITED ARAB EMIRATES - Tags: SPORT TENNIS) 

Dmitry Tursunov of Russia returns the ball to Lukas Lacko of Slovakia during their men's singles match at the ATP Dubai Tennis Championships, February 24, 2014. REUTERS/Saleh Salem (UNITED ARAB EMIRATES - Tags: SPORT TENNIS) 

Dmitry Tursunov of Russia returns the ball to Lukas Lacko of Slovakia during their men's singles match at the ATP Dubai Tennis Championships, February 24, 2014. REUTERS/Saleh Salem (UNITED ARAB EMIRATES - Tags: SPORT TENNIS) 

Lukas Lacko of Slovakia returns the ball to Dmitry Tursunov of Russia during their men's singles match at the ATP Dubai Tennis Championships, February 24, 2014. REUTERS/Saleh Salem (UNITED ARAB EMIRATES - Tags: SPORT TENNIS) 

Juan Martin Del Potro of Argentina hits a return to Dmitry Tursunov of Russia during their men's singles semi-final match at the Sydney International tennis tournament, January 10, 2014. REUTERS/Jason Reed (AUSTRALIA - Tags: SPORT TENNIS) 

Dmitry Tursunov of Russia sits on the court after slipping during a return to Juan Martin Del Potro of Argentina in their men's singles semi-final match at the Sydney International tennis tournament, January 10, 2014. REUTERS/Jason Reed (AUSTRALIA - Tags: SPORT TENNIS) 

Juan Martin Del Potro of Argentina hits a return to Dmitry Tursunov of Russia during their men's singles semi-final match at the Sydney International tennis tournament, January 10, 2014. REUTERS/Jason Reed (AUSTRALIA - Tags: SPORT TENNIS) 

Juan Martin Del Potro of Argentina acknowledges the crowd after defeating Dmitry Tursunov of Russia in their men's singles semi-final match at the Sydney International tennis tournament, January 10, 2014. REUTERS/Jason Reed (AUSTRALIA - Tags: SPORT TENNIS) 

Juan Martin Del Potro of Argentina blows a kiss skyward after defeating Dmitry Tursunov of Russia in their men's singles semi-final match at the Sydney International tennis tournament, January 10, 2014. REUTERS/Jason Reed (AUSTRALIA - Tags: SPORT TENNIS) 

Roger Federer of Switzerland crouches down while his partner Zhang Ze of China serves to Kevin Anderson of South Africa and Dmitry Tursunov of Russia during their men's doubles match at the Shanghai Masters tennis tournament October 7, 2013. REUTERS/Aly Song (CHINA - Tags: SPORT TENNIS) 

Roger Federer (R) of Switzerland and Zhang Ze of China talk during their men's doubles match against Kevin Anderson of South Africa and Dmitry Tursunov of Russia at the Shanghai Masters tennis tournament, October 7, 2013. REUTERS/Aly Song (CHINA - Tags: SPORT TENNIS) 

Roger Federer (R) of Switzerland, with his partner Zhang Ze of China, hits a return to Kevin Anderson of South Africa and Dmitry Tursunov of Russia during their men's doubles match at the Shanghai Masters tennis tournament October 7, 2013. REUTERS/Aly Song (CHINA - Tags: SPORT TENNIS) 

Roger Federer of Switzerland (R), with his partner Zhang Ze of China, hits a return to Kevin Anderson of South Africa and Dmitry Tursunov of Russia during their men's doubles match at the Shanghai Masters tennis tournament October 7, 2013. REUTERS/Aly Song (CHINA - Tags: SPORT TENNIS) 

Roger Federer (top) of Switzerland, with his partner Zhang Ze of China, hits a return to Kevin Anderson of South Africa and Dmitry Tursunov of Russia during their men's doubles match at the Shanghai Masters tennis tournament October 7, 2013. REUTERS/Aly Song (CHINA - Tags: SPORT TENNIS) 

Richard Gasquet of France shouts out during his match against Dmitry Tursunov of Russia at the U.S. Open tennis championships in New York August 31, 2013. REUTERS/Eduardo Munoz (UNITED STATES - Tags: SPORT TENNIS) 

Richard Gasquet of France serves to Dmitry Tursunov of Russia at the U.S. Open tennis championships in New York August 31, 2013. REUTERS/Eduardo Munoz (UNITED STATES - Tags: SPORT TENNIS) 

Dmitry Tursunov of Russia serves to Richard Gasquet of France at the U.S. Open tennis championships in New York August 31, 2013. REUTERS/Eduardo Munoz (UNITED STATES - Tags: SPORT TENNIS)

Richard Gasquet of France serves to Dmitry Tursunov of Russia at the U.S. Open tennis championships in New York August 31, 2013. REUTERS/Eduardo Munoz (UNITED STATES - Tags: SPORT TENNIS)

Richard Gasquet of France returns to Dmitry Tursunov of Russia at the U.S. Open tennis championships in New York August 31, 2013. REUTERS/Eduardo Munoz (UNITED STATES - Tags: SPORT TENNIS)

Richard Gasquet of France serves to Dmitry Tursunov of Russia at the U.S. Open tennis championships in New York August 31, 2013. REUTERS/Eduardo Munoz (UNITED STATES - Tags: SPORT TENNIS)

Richard Gasquet of France serves to Dmitry Tursunov of Russia at the U.S. Open tennis championships in New York August 31, 2013. REUTERS/Eduardo Munoz (UNITED STATES - Tags: SPORT TENNIS)

Richard Gasquet of France returns to Dmitry Tursunov of Russia at the U.S. Open tennis championships in New York August 31, 2013. REUTERS/Eduardo Munoz (UNITED STATES - Tags: SPORT TENNIS)

Sweat falls from the face of Richard Gasquet of France as he waits for a serve from Dmitry Tursunov of Russia at the U.S. Open tennis championships in New York August 31, 2013. REUTERS/Eduardo Munoz (UNITED STATES - Tags: SPORT TENNIS)