Caroline Wozniacki of Denmark tries to hit a return as her hair gets caught in her racquet while playing Aliaksandra Sasnovich of Belarus during the third day of the 2014 US Open Tennis Championship at the USTA National Tennis Center in Flushing Meadows, New York, USA, 27 August 2014. The US Open runs through 08 September, a 15-day schedule. EPA/JOHN G. MABANGLO

Gael Monfils of France in action against Andy Murray of Britain during their match at the first leg of International Tennis Premier League (IPTL) at the Mall of Asia Arena in Pasay city, south of Manila, Philippines, 29 November 2014. EPA/RITCHIE B. TONGO

Roger Federer of Switzerland hits a return to Marin Cilic of Croatia during their semifinals round match on the thirteenth day of the 2014 US Open Tennis Championship at the USTA National Tennis Center in Flushing Meadows, New York, USA, 06 September 2014. The US Open runs through 08 September, a 15-day schedule. EPA/JUSTIN LANE

Serena Williams of the USA returns the ball to Jelena Jankovic of Serbia during their quarter final match of the Dubai Duty Free Tennis WTA Championships in Dubai, United Arab Emirates, 20 February 2014. EPA/ALI HAIDER

Novak Djokovic of Serbia falls to the court as he celebrates defeating Rafael Nadal of Spain following their men’s singles final match at the Sony Open tennis tournament on Key Biscayne in Miami, Florida, USA, 30 March 2014. EPA/RHONA WISE

Rafael Nadal of Spain in action against Grigor Dimitrov of Bulgaria during their quarter final match of the Australian Open Grand Slam tennis tournament in Melbourne, Australia, 22 January 2014. EPA/JOE CASTRO AUSTRALIA AND NEW ZEALAND OUT