NEW YORK (Reuters) - A bitterly disappointed Andy Murray was at a loss to explain why his body failed him at the U.S. Open on Sunday and left him wondering whether he will ever fulfill his dream of winning a grand slam title.
The Scot's movement was clearly impaired from early in the third set of his third-round clash with Swiss 25th seed Stanislas Wawrinka and he slumped to a 6-7 7-6 6-3 6-3 defeat.
Murray had treatment to his left thigh midway through the third set and several times afterwards and in the fourth set he needed help from the trainer after complaining of tingling in his right arm.
He was at pains not to make excuses but was unable to hide his disappointment and confusion at why he was not at 100 percent.
"I just didn't feel great," Murray said. "There were a lot of things that I was feeling on the court. I just haven't felt that way for a few years now, so I'm going to have to go look at why that was the case and try and get better."
Murray came close to winning his first grand slam title in January when he reached the final of the Australian Open, losing to Roger Federer.
He was beaten by Rafa Nadal in the semi-finals at Wimbledon but went into the U.S. Open as one of the favorites, having won the Masters 1000 title in Toronto.
But the 23-year-old admitted that he could not guarantee that he will succeed at the highest level.
"I have no idea whether I'll win a grand slam or not," he said. "I want to, but if I never win one, then what?
"If I give a hundred percent, try my best, physically work as hard as I can, practice as much as I can, then that's all I can do.
"It's something I would love to do. It's a very difficult thing. But I'll give it my best shot."
Murray, who said he first started having problems early in the third set, is renowned as one of the fittest players on the tour.
But as the tightness set in, he was unable to move as well as he had been in the first two sets and Wawrinka, who had thigh problems of his own, slowly got the better of him.
"In the third and fourth sets I was struggling physically and I got frustrated with that," Murray said. "I tried to come back and didn't quite do it.
"I've worked very hard to give myself a chance of winning tournaments. When I was struggling physically, I got disappointed. But I'm sorry, that happens.
"It happens to everyone in life at different points. I just struggled in the third and fourth sets today. That's it."
Murray said the loss to Wawrinka was the most disappointing of his four grand slam defeats this year.
"I've had two very good majors and two where I haven't been so good," he said.
"But I've lost to Roger, who's probably the best ever. I lost to Rafa, who I think will be the second best -- if not the best -- ever and to (Tomas) Berdych (at the French Open), who played great tennis this year."
"This summer overall, I played some great tennis again. I'm just disappointed I didn't play my greatest tennis here."
Editing by Steve Ginsburg