Jean Michel Saive of Belgium eyes the ball during his first round singles table tennis match at the 1st European Games in Baku, Azerbaijan, June 16 , 2015. REUTERS/Stoyan Nenov TPX IMAGES OF THE DAY

Novak Djokovic of Serbia eyes the ball as he prepares to play a shot to Jarkko Nieminen of Finland during their men's singles match at the French Open tennis tournament at the Roland Garros stadium in Paris, France, May 26, 2015. REUTERS/Pascal Rossignol TPX IMAGES OF THE DAY

Rafael Nadal of Spain serves to Kevin Anderson of South Africa during their men's singles fourth round match at the Australian Open 2015 tennis tournament in Melbourne January 25, 2015. REUTERS/Athit Perawongmetha (AUSTRALIA - Tags: SPORT TENNIS TPX IMAGES OF THE DAY)

REFILE - USING ENGLISH SPELLING OF BELARUS Caroline Wozniacki of Denmark returns to Victoria Azarenka of Belarus during their second round match at the Rome Open tennis tournament in Rome, Italy, May 13, 2015. REUTERS/Max Rossi TPX IMAGES OF THE DAY 

Roger Federer of Switzerland eyes the ball during his tennis match against Pablo Cuevas of Uruguay at the Rome Open tennis tournament in Rome, Italy, May 13, 2015. REUTERS/Max Rossi TPX IMAGES OF THE DAY

China's Ma Long serves against South Korea's Joo Sae-hyuk in their men's singles fourth round match at the World Table Tennis Championships in Suzhou, Jiangsu province May 1, 2015. REUTERS/Aly Song TPX IMAGES OF THE DAY

Luka Bakic of Montenegro eyes the ball as he serves to Timothy Wang of the U.S. during the qualification round match at the World Table Tennis Championships in Suzhou, Jiangsu province April 27, 2015. REUTERS/Aly Song 

Maria Sharapova of Russia stretches to hit a return to Serena Williams of the U.S. during their women's singles final match at the Australian Open 2015 tennis tournament in Melbourne January 31, 2015. REUTERS/Thomas Peter (AUSTRALIA - Tags: SPORT TENNIS TPX IMAGES OF THE DAY)

Andy Murray of Britain eyes the ball before hitting a return to Tomas Berdych of Czech Republic during men's singles semi-final match at the Australian Open 2015 tennis tournament in Melbourne January 29, 2015. REUTERS/Thomas Peter (AUSTRALIA - Tags: SPORT TENNIS)

Grigor Dimitrov of Bulgaria eyes the ball as he prepares to hit a return to Marcos Baghdatis of Cyprus during their men's singles third round match at the Australian Open 2015 tennis tournament in Melbourne January 23, 2015. REUTERS/Brandon Malone (AUSTRALIA - Tags: SPORT TENNIS)

Mona Barthel of Germany prepares to hit a return against Petra Kvitova of Czech Republic during their women's singles second round match at the Australian Open 2015 tennis tournament in Melbourne January 22, 2015. REUTERS/Thomas Peter (AUSTRALIA - Tags: SPORT TENNIS TPX IMAGES OF THE DAY)

Iraq's Younus Mahmood eyes the ball during their Asian Cup Group D soccer match against Jordan at the Brisbane Stadium in Brisbane January 12, 2015. REUTERS/Edgar Su (AUSTRALIA - Tags: SOCCER SPORT)

Madison Keys of the United States hits a return to Dominika Cibulkova of Slovakia during their Brisbane International tennis tournament first round match in Brisbane, January 5, 2015. REUTERS/Jason Reed (AUSTRALIA - Tags: SPORT TENNIS TPX IMAGES OF THE DAY)