Tennis - Wimbledon - All England Lawn Tennis and Croquet Club, London, Britain - July 11, 2018. Switzerland's Roger Federer's wears Uniqlo branded socks and Nike tennis shoes during his quarter final match against South Africa's Kevin Anderson. REUTERS/Andrew Boyers 

Tennis - Wimbledon - All England Lawn Tennis and Croquet Club, London, Britain - July 9, 2018. Switzerland's Roger Federer wears Uniqlo socks and Nike shoes during his fourth round match against France's Adrian Mannarino. REUTERS/Toby Melville 

Tennis - Wimbledon - All England Lawn Tennis and Croquet Club, London, Britain - July 9, 2018. Switzerland's Roger Federer wears Uniqlo socks and Nike shoes during his fourth round match against France's Adrian Mannarino. REUTERS/Toby Melville 

Tennis - Wimbledon - All England Lawn Tennis and Croquet Club, London, Britain - July 9, 2018. Switzerland's Roger Federer wears Uniqlo socks and Nike shoes during his fourth round match against France's Adrian Mannarino. REUTERS/Toby Melville 

Tennis - Wimbledon - All England Lawn Tennis and Croquet Club, London, Britain - July 2, 2018 Switzerland's Roger Federer in action during the first round match against Serbia's Dusan Lajovic. REUTERS/Andrew Boyers 

Switzerland's Roger Federer casts a shadow as he serves during his quarter-final match against Czech Republic's Tomas Berdych at the Australian Open tennis tournament at Melbourne Park, Australia, January 26, 2016. REUTERS/Jason Reed 

Switzerland's Roger Federer casts a shadow as he serves during his quarter-final match against Czech Republic's Tomas Berdych at the Australian Open tennis tournament at Melbourne Park, Australia, January 26, 2016. REUTERS/Jason Reed TPX IMAGES OF THE DAY 

Switzerland's Roger Federer casts a shadow as he serves during his quarter-final match against Czech Republic's Tomas Berdych at the Australian Open tennis tournament at Melbourne Park, Australia, January 26, 2016. REUTERS/Jason Reed 

Switzerland's Roger Federer wipes his forehead during his quarter-final match against Czech Republic's Tomas Berdych at the Australian Open tennis tournament at Melbourne Park, Australia, January 26, 2016. REUTERS/Tyrone Siu 

Georgia's Nikoloz Basilashvili hits a shot during his first round match against Switzerland's Roger Federer at the Australian Open tennis tournament at Melbourne Park, Australia, January 18, 2016. REUTERS/Jason Reed 

Tennis - Barclays ATP World Tour Finals - O2 Arena, London - 22/11/15
Men's Singles Final - Switzerland's Roger Federer in action against Serbia's Novak Djokovic
Action Images via Reuters / Tony O'Brien
Livepic
EDITORIAL USE ONLY. 

Tennis - Barclays ATP World Tour Finals - O2 Arena, London - 22/11/15
Men's Singles Final - Switzerland's Roger Federer looks dejected during his match with Serbia's Novak Djokovic
Reuters / Suzanne Plunkett
Livepic
EDITORIAL USE ONLY. 

Tennis - Barclays ATP World Tour Finals - O2 Arena, London - 22/11/15
Men's Singles Final - Switzerland's Roger Federer looks dejected during his match with Serbia's Novak Djokovic
Reuters / Suzanne Plunkett
Livepic
EDITORIAL USE ONLY. 

Tennis - Barclays ATP World Tour Finals - O2 Arena, London - 19/11/15
Men's Singles - Switzerland's Roger Federer in action during his match against Japan's Kei Nishikori
Action Images via Reuters / Tony O'Brien
Livepic
EDITORIAL USE ONLY. 

Tennis - Barclays ATP World Tour Finals - O2 Arena, London - 19/11/15
Men's Singles - Switzerland's Roger Federer in action during his match against Japan's Kei Nishikori
Reuters / Suzanne Plunkett
Livepic
EDITORIAL USE ONLY. 

Tennis - Barclays ATP World Tour Finals - O2 Arena, London - 19/11/15
Men's Singles - Switzerland's Roger Federer during his match against Japan's Kei Nishikori
Reuters / Suzanne Plunkett
Livepic
EDITORIAL USE ONLY. 

Tennis - Barclays ATP World Tour Finals - O2 Arena, London - 19/11/15
Men's Singles - Switzerland's Roger Federer during his match against Japan's Kei Nishikori
Action Images via Reuters / Tony O'Brien
Livepic
EDITORIAL USE ONLY. 

Roger Federer of Switzerland wears his signature shoe from Nike as he plays compatriot Stan Wawrinka during their men's singles semi-final match at the U.S. Open Championships tennis tournament in New York, September 11, 2015. REUTERS/Shannon Stapleton 

The shoes of Roger Federer of Switzerland are seen as he jumps to play a shot to Damir Dzumhur of Bosnia and Herzegovina during their men's singles match at the French Open tennis tournament at the Roland Garros stadium in Paris, France, May 29, 2015. REUTERS/Gonzalo Fuentes

Roger Federer of Switzerland waits to announce that he is injured and unfit to play Novak Djokovic of Serbia in the men's singles final tennis match at the ATP World Tour Finals at the O2 in London, November 16, 2014. REUTERS/Dylan Martinez (BRITAIN - Tags: SPORT TENNIS TPX IMAGES OF THE DAY) 

Roger Federer of Switzerland serves while wearing a new shoe, the Nike Zoom Vapor 9 Tour AJ3 he helped design with basketball great Michael Jordan, during his men's singles match against Marinko Matosevic of Australia at the U.S. Open tennis tournament in New York August 26, 2014. REUTERS/Shannon Stapleton (UNITED STATES - Tags: SPORT TENNIS) 

Roger Federer of Switzerland debuts a new shoe, the Nike Zoom Vapor 9 Tour AJ3 he helped design with basketball great Michael Jordan, as he plays Marinko Matosevic of Australia during their men's singles match at the U.S. Open tennis tournament in New York August 26, 2014. REUTERS/Shannon Stapleton (UNITED STATES - Tags: SPORT TENNIS SOCIETY) 

Four Swiss flags, which represent the four Australian Open titles that Roger Federer of Switzerland won, are seen on his shoes during his match against Xavier Malisse of Belgium at the Australian Open tennis tournament in Melbourne January 21, 2011. REUTERS/Tim Wimborne (AUSTRALIA - Tags: SPORT TENNIS) 

Switzerland's Roger Federer reacts during his Paris Masters tennis tournament match against Radek Stepanek of the Czech Republic, November 11, 2010. REUTERS/Benoit Tessier (FRANCE - Tags: SPORT TENNIS) 

Roger Federer wears shoes displaying the skyline of New York while playing Andreas Beck of Germany during the U.S. Open tennis tournament in New York, September 2, 2010. REUTERS/Kevin Lamarque (UNITED STATES - Tags: SPORT TENNIS) 

Roger Federer of Switzerland prepares on Centre Court before his match against Philipp Kohlschreiber of Germany at the Wimbledon tennis championships, in London June 26, 2009. REUTERS/Toby Melville (BRITAIN SPORT TENNIS) 

Roger Federer of Switzerland prepares on Centre Court before his match against Philipp Kohlschreiber of Germany at the Wimbledon tennis championships, in London June 26, 2009. REUTERS/Toby Melville (BRITAIN SPORT TENNIS) 

Roger Federer of Switzerland plays a shot during his match against Alberto Martin of Spain at the French Open tennis tournament at Roland Garros in Paris May 25, 2009. REUTERS/Benoit Tessier (FRANCE SPORT TENNIS) 

Spain's Rafael Nadal returns to Switzerland's Roger Federer during their men's singles final match at the Australian Open tennis tournament in Melbourne February 1, 2009. Picture taken with a slow shutter speed. REUTERS/Daniel Munoz (AUSTRALIA) 

Switzerland's Roger Federer wipes the sweat away from his face during his match against Czech Republic's Tomas Berdych at the Australian Open tennis tournament in Melbourne January 25, 2009. REUTERS/Daniel Munoz (AUSTRALIA) 

Switzerland's Roger Federer pulls on a new shirt with the neck button still done up during his match against Russia's Marat Safin at the Australian Open tennis tournament in Melbourne January 23, 2009. REUTERS/Tim Wimborne (AUSTRALIA) 

Switzerland's Roger Federer celebrates his victory over Argentina's David Nalbandian in their final match at the Swiss Indoors ATP tennis tournament in Basel October 26, 2008. REUTERS/ Christian Hartmann (SWITZERLAND) 

The shoes of Roger Federer of Switzerland are seen during the men's final match against Andy Murray of Britain at the U.S. Open tennis tournament at Flushing Meadows in New York September 8, 2008. REUTERS/Eduardo Munoz (UNITED STATES) 

Roger Federer of Switzerland returns a shot to Gilles Muller of Luxembourg during their quarterfinal match at the U.S. Open tennis tournament in Flushing Meadows in New York September 4, 2008. REUTERS/Jeff Haynes (UNITED STATES) 

Roger Federer of Switzerland waits for the serve from Igor Andreev of Russia during their match at the U.S. Open tennis tournament in Flushing Meadows in New York, September 2, 2008. REUTERS/Shaun Best (UNITED STATES) 

Tennis players Roger Federer (L) and Rafael Nadal (R), and presenter Don King pose during the "Grapple In The Apple" Nike event at the Mandarin Oriental Hotel in New York August 21, 2008. REUTERS/Joshua Lott (United States) 

Tennis players Roger Federer (L) and Rafael Nadal (R), and presenter Don King pose during the "Grapple In The Apple" Nike event at the Mandarin Oriental Hotel in New York August 21, 2008. REUTERS/Joshua Lott (United States) 

Tennis players Roger Federer (L) and Rafael Nadal attend the "Grapple In The Apple" Nike event at the Mandarin Oriental Hotel in New York August 21, 2008. REUTERS/Joshua Lott (United States) 

Tennis player Roger Federer attends the "Grapple In The Apple" Nike event at the Mandarin Oriental Hotel in New York August 21, 2008. REUTERS/Joshua Lott (UNITED STATES) 

Tennis player Roger Federer attends the "Grapple In The Apple" Nike event at the Mandarin Oriental Hotel in New York August 21, 2008. REUTERS/Joshua Lott (UNITED STATES) 

Tennis players Rafael Nadal (L) and Roger Federer attend the "Grapple In The Apple" Nike event at the Mandarin Oriental Hotel in New York August 21, 2008. REUTERS/Joshua Lott (UNITED STATES) 

Roger Federer of Switzerland follows through on a shot to Gilles Simon of France at the Rogers Cup tennis tournament in Toronto July 23, 2008. REUTERS/Mark Blinch (CANADA) 

Spare shoes and a racquet sit beside the chair of Rafael Nadal of Spain as he practices at Wimbledon, London, July 5, 2008. Nadal will play Roger Federer in the men's final of the Wimbledon tennis championship on Sunday. REUTERS/Kevin Lamarque (BRITAIN) 

The feet of Roger Federer of Switzerland are seen as he serves to Mario Ancic of Croatia during their quarter-finals match at the Wimbledon tennis championships in London July 2, 2008. REUTERS/Toby Melville (BRITAIN) 

Detail is seen on the back of Switzerland's Roger Federer's shoe as he trains on the practice courts at Wimbledon, ahead of the Wimbledon Tennis Championships in south London June 21, 2008. REUTERS/Toby Melville (BRITAIN) 

Spain's Rafael Nadal returns the ball to Switzerland's Roger Federer during their men's final French Open tennis tournament at Roland Garros in Paris June 8, 2008. REUTERS/Regis Duvignau (FRANCE) also see: PM1E486198U01 

Switzerland's Roger Federer celebrates after defeating Chile's Fernando Gonzalez during their quarter-final match at the French Open tennis tournament at Roland Garros in Paris June 4, 2008. REUTERS/Francois Lenoir (FRANCE) 

Switzerland's Roger Federer celebrates after defeating Chile's Fernando Gonzalez during their quarter-final match at the French Open tennis tournament at Roland Garros in Paris June 4, 2008. REUTERS/Francois Lenoir (FRANCE) 

Roger Federer of Switzerland reacts during his tennis match against Victor Hanescu of Romania at the Estoril Open in Lisbon April 17, 2008. REUTERS/Hugo Correia (PORTUGAL) 

Roger Federer of Switzerland hits a return to Rafael Nadal of Spain during their semi-final match at the Masters Cup tennis tournament in Shanghai November 17, 2007. REUTERS/ Nir Elias (CHINA) 

Roger Federer of Switzerland celebrates a point against Novak Djokovic of Serbia during the men's final of the U.S. Open tennis tournament in Flushing Meadows, New York, September 9, 2007. REUTERS/Mike Segar (UNITED STATES) 

Roger Federer of Switzerland yells after winning the second set against Feliciano Lopez of Spain during their match at the U.S. Open tennis tournament in Flushing Meadows, New York, September 3, 2007. REUTERS/Shannon Stapleton (UNITED STATES) 

Roger Federer of Switzerland serves to James Blake of the United States during their championship match at the 2007 Cincinnati Masters tennis tournament in Cincinnati, Ohio, August 19, 2007. REUTERS/John Sommers II (UNITED STATES) 

Switzerland's Roger Federer lies on the court after winning the men's singles final against Spain's Rafael Nadal at the Wimbledon tennis championships in London, July 8, 2007. REUTERS/Eddie Keogh (BRITAIN) 

Switzerland's Roger Federer serves to Argentina's Juan Martin Del Potro during their singles match at the Wimbledon tennis championships in London, June 27, 2007. REUTERS/Toby Melville (BRITAIN) 

Roger Federer of Switzerland rests during his match against Guillermo Canas of Argentina at the Sony Ericsson Open tennis tournament in Key Biscayne, Miami March 27, 2007. Federer suffered a stunning 7-6 2-6 7-6 defeat by Canas on Tuesday, the world number one's second loss to the Argentine in successive tournaments. REUTERS/Carlos Barria (UNITED STATES) 

Roger Federer changes his t-shirt during a match against Guillermo Canas of Argentina at the Sony Ericsson Open tennis tournament in Key Biscayne, Miami March 27, 2007. REUTERS/Carlos Barria (UNITED STATES) 

Switzerland's Roger Federer wipes his brow after losing a point during his loss to Argentina's Guillermo Canas at the Pacific Life Open tennis tournament in Indian Wells, California March 11, 2007. The loss ended Federer's streak of 41 consecutive victories. REUTERS/Danny Moloshok (UNITED STATES) 

Roger Federer of Switzerland serves to Andre Agassi of the U.S. during the men's final at the U.S. Open tennis tournament in Flushing Meadows, New York, September 11, 2005. REUTERS/Lucy Nicholson JA/DY 

Roger Federer of Switzerland serves to Andre Agassi of the U.S. During the men's final at the U.S. Open tennis tournament in Flushing Meadows, New York, September 11, 2005. Pictures of the Year 2005 REUTERS/Lucy Nicholson JA/DY