Roger Federer, of Switzerland, right, and Tommy Robredo, of Spain, walk off the court during a break in play during the fourth round of the 2013 U.S. Open tennis tournament, Monday, Sept. 2, 2013, in New York. (AP Photo/Darron Cummings)
Roger Federer, of Switzerland, returns a shot to Grega Zemlja, of Slovenia, during the first round of the 2013 U.S. Open tennis tournament Tuesday, Aug. 27, 2013, in New York. (AP Photo/Mike Groll)
Roger Federer, from Switzerland, hits a backhand against Tommy Haas, from Germany, during a match at the Western & Southern Open tennis tournament, Thursday, Aug. 15, 2013, in Mason, Ohio. (AP Photo/Al Behrman)
Roger Federer of Switzerland reacts during his match against Daniel Brands of Germany, a second round match at the Suisse Open tennis tournament in Gstaad, Switzerland, Thursday July 25, 2013. (AP Photo/Keystone/Peter Schneider)
Sergiy Stakhovsky of Ukraine reacts after winning the third set against Roger Federer of Switzerland during their Men's second round singles match at the All England Lawn Tennis Championships in Wimbledon, London, Wednesday, June 26, 2013. (AP Photo/Alastair Grant)