Roger Federer said his troubled preparations for the US Open was the main reason for him crashing out of the quarter-final's against Juan Martin Del Potro on Wednesday.
The 36-year-old Swiss lost 7-5, 3-6, 7-6(8), 6-4 in a thrilling encounter at Arthur Ashe Stadium.
In a press conference after his defeat, Federer, who was forced to was forced to withdraw from playing in US Open warm-up tournaments because of back pain, said he had spent most of the time leading up to the tournament worrying about his back instead of focusing on training.
"The best player won today, by far, and I don't have a problem with that," said Federer.
"I don't want to take anything from Juan Martin but when you get injured before a tournament, you are not focused on training or on how to play during the tournament.
"It was a bit the case for me before the U.S. Open. Then I had to play a couple of five setters and you start to hurt a little bit everywhere."
Having won the Australian Open and Wimbledon earlier this year, Federer went into the US Open as a lot of peoples favourite to claim the final slam of the year and cap off a brilliant 2017, but added that he felt he never really reached that level in New York.
"I never had the feeling I had reached the level I wanted. I forced myself to think that but I never had quite the same rhythm as during the Australian Open, Wimbledon, Indian Wells or Miami," he added.
"I've been forced to kind of protect my service games. I was never really safe and I knew that there would always be one or two service games where I would be in danger."
"I did not play badly in the first set but I was weak at the end of it and that set costs me the match at the end of the day.
"That put me in a position where I needed some luck, where the margins were really tight."
"I feel I have no place in the semis and he (Del Potro) will have a better chance to beat Rafa (Nadal), to be honest," he added.