The two-time grand slam winner has not looked at his best since his emotional win over Novak Djokovic at the All England Club in July and he conceded that he has since found it tough to get motivated.
"When you work hard for something for a lot of years, it's going to take a bit of time to really fire yourself up and get yourself training (at) 110 percent," the British third seed told reporters after his 6-4 6-3 6-2 loss to ninth-seeded Wawrinka.
"That's something that I think is kind of natural after what happened at Wimbledon. But I got here. I mean, I have been here nearly three weeks now.
"I practiced a lot, and played quite a lot of matches, as well. So I gave myself a chance to do well because I prepared properly."
It has been a breakthrough year for Murray who has won Olympic gold, the U.S. Open and Wimbledon, in the past 13 months.
"I have played my best tennis in the slams the last two, three years. I lost today in straight sets, so that's disappointing. I would have liked to have gone further," said Murray.
"But I can't complain. If someone told me before the U.S. Open last year I would have been here as defending champion having won Wimbledon and Olympic gold, I would have taken that 100 percent."
The Scotsman's victory at Wimbledon was amplified by the pressure of ending Britain's 77-year wait for a winner in their own tournament and the celebrations and accolades it brought.
But while it would be going too far to suggest Murray is burnt out there is no doubt that his recent form has been well below his own lofty standards.
He lost to Latvian Ernest Gulbis in the third round at Montreal and was beaten in straight sets by Czech Tomas Berdych in the Cincinnati Masters event last month.
While he reached the quarter-finals at Flushing Meadows without any major scare there looked to be a clear lack of sparkle about his play.
Murray said winning Wimbledon had been a physically and mentally draining experience.
"It's been challenging both ways for different reasons. I mean, physically I played some extremely tough matches in that period," said Murray.
"Mentally, as well, it was very challenging for me to play Wimbledon. The last few games of Wimbledon to you guys may not seem like much, but to me it was extremely challenging."
Murray has been extremely consistent in grand slams, having reached the last eight in each one he entered in the past three years and his most recent four have produced two wins and two runners-up spots.
But it is clear that brings increased expectation which Murray suggested might not be fair.
"Well, I don't know; if I'm meant to win every grand slam I play or be in the final, it's just very, very difficult just now," he said. "With the guys around us, it's very challenging." (Editing by Frank Pingue)