Roger Federer of Switzerland wraps his face with hands while walking off the court after losing the men's singles fourth round match against Tommy Robredo of Spain at the 2013 US Open tennis championships in New York, the United States, on Sept. 2, 2013. Robredo won 3-0. (Xinhua/Wang Lei)

Roger Federer of Switzerland reacts during the press conference after the men's singles fourth round match against Tommy Robredo of Spain at the 2013 US Open tennis championships in New York, the United States, on Sept. 2, 2013. Robredo won 3-0. (Xinhua/Fang Zhe)

Roger Federer of Switzerland hits a return during the men's singles fourth round match against Tommy Robredo of Spain at the 2013 US Open tennis championships in New York, the United States, on Sept. 2, 2013. Robredo won 3-0. (Xinhua/Wang Lei)

Roger Federer of Switzerland reacts during the men's singles fourth round match against Tommy Robredo of Spain at the 2013 US Open tennis championships in New York, the United States, on Sept. 2, 2013. Robredo won 3-0. (Xinhua/Wang Lei)

Roger Federer of Switzerland hits a return during the men's singles fourth round match against Tommy Robredo of Spain at the 2013 US Open tennis championships in New York, the United States, on Sept. 2, 2013. Robredo won 3-0. (Xinhua/Wang Lei)

Roger Federer (R) of Switzerland greets Tommy Robredo of Spain after the men's singles fourth round match at the 2013 US Open tennis championships in New York, the United States, on Sept. 2, 2013. Robredo won 3-0. (Xinhua/Wang Lei)

Roger Federer of Switzerland waves to the audience after the men's singles fourth round match against Tommy Robredo of Spain at the 2013 US Open tennis championships in New York, the United States, on Sept. 2, 2013. Robredo won 3-0. (Xinhua/Wang Lei)

Roger Federer of Switzerland reacts after losing the men's singles fourth round match against Tommy Robredo of Spain at the 2013 US Open tennis championships in New York, the United States, on Sept. 2, 2013. Robredo won 3-0. (Xinhua/Wang Lei)

Roger Federer of Switzerland reacts during the men's singles fourth round match against Tommy Robredo of Spain at the 2013 US Open tennis championships in New York, the United States, on Sept. 2, 2013. Robredo won 3-0. (Xinhua/Wang Lei)