Andy Murray has pulled out of the US Open two days before the start of the tournament in New York after failing to recover from a hip injury.
The British world number two, 30, has not played since Wimbledon when he was hampered by the injury as he lost to Sam Querrey in the quarter-finals.
Murray practised all week but said on Saturday the injury remained an issue.
"It's too sore for me to win the tournament and ultimately that's what I was here to try and do," said the Scot.
The 2012 US Open champion was due to face American world number 104 Tennys Sandgren in the first round.
It is the first time since the French Open in 2013 that Murray has withdrawn from a Grand Slam tournament.
He revealed during Wimbledon that he had suffered with a sore hip at times since his early twenties, but it became more significant following his French Open semi-final loss against Stan Wawrinka in June.
Murray's preparation for Wimbledon was cut back and he ultimately succumbed to Querrey in five sets at the All England Club.
He was forced to pull out of tournaments in Montreal and Cincinnati as he underwent rehabilitation in the UK, but travelled to New York on 18 August with the expectation of playing the US Open.
"I did pretty much everything that I could to get myself ready here and took a number of weeks off after Wimbledon," added Murray, who has lost the world number one ranking to Rafael Nadal since Wimbledon.
"I obviously spoke to a lot of hip specialists. Tried resting, rehabbing, to try and get myself ready here.
"I was actually practising OK the last few days."
Asked if he had risked potential further damage by attempting to play at Flushing Meadows, Murray added: "I certainly wouldn't have been hurting myself more by trying to play. It was more a question of whether it would settle down in time.
"Obviously I kind of ran out of time. Maybe if I'd been able to take a little bit more time off."
Murray joins last year's finalists Wawrinka and Novak Djokovic - both of whom have chosen to end their seasons because of injuries - in a lengthy list of absentees in New York, but he hopes to return to action in 2017.
Croatian fifth seed Marin Cilic will move up to Murray's place in the draw and face Sandgren in the first round on Monday.
By Russell Fuller, BBC tennis correspondent at Flushing Meadows:
A slight limp was still visible when Murray took to the practice court on Saturday lunchtime. He was striking the ball well against Lucas Pouille and looked in better shape than he had done at the same stage before Wimbledon, but there was a zip and intensity missing from the session - for good reason, as it now appears.
Perhaps Murray could have made this decision 10 days ago before flying to New York to step up his preparations, but better late than never. There is no point in him playing an event he has virtually no chance of winning, however open the draw may seem.
Having already consulted a range of specialists, Murray sounded quite sure he would be able to decide on his next move over the next couple of days. He did not address the need for surgery, but surely it remains an option, and perhaps we will not see him again this year.
Whatever the plan, Murray's focus must now be entirely on 2018. He will not win Grand Slams if he is only 80% fit, and unable to move with the speed and purpose which have brought him so much success thus far.
Following Murray's Wimbledon exit in July, BBC Sport pundit and six-time Grand Slam winner Boris Becker advised Murray to consider skipping the US Open.
"Age is only a number, but you only have one body. Andy has to look after his," said Becker.
"He has got to think long term, not worry about making the US Open - if he is moving there like he did at Wimbledon, then he won't win it anyway.
"So, the worst thing that can happen if he skips New York is that he misses one Grand Slam - that doesn't matter, because the Australian Open is around the corner at the start of 2018."
Becker said Murray could learn from Nadal and Roger Federer, both of whom took long breaks from the game before returning fitter.
Nadal pulled out of the French Open in May 2016 with a wrist injury and did not play again until the Rio Olympics in August. He won his 10th title at Roland Garros earlier this year.
Federer missed the final five months of 2016 to recover from his knee injury but returned to win the Australian Open in January and Wimbledon in July.
"With this injury, there are limitations to Andy's movement," said Becker. "Andy relies on his speed and footwork, which are an integral part of his game.
"That is why he needs to be 100% fit. It's no good for him to be 75%."