Ronnie O'Sullivan has pulled out of the International Championship in China, citing "ongoing health problems".
The world champion was due to end a four-month hiatus from ranking competition at the Chengdu event.
He said in a statement: "I would have loved to be fit to compete in Chengdu, but I have been advised by my doctor not to travel.
"I want to sincerely apologise to World Snooker, the sponsors and the fans for the disappointment caused."
O'Sullivan's withdrawal is a major blow to the richest tournament China will have ever staged, with the winner collecting £125,000 from a total prize fund of £600,000.
Jason Ferguson, chairman of the World Professional Billiards and Snooker Association, said: "This is a huge disappointment for all of the fans in China who were hoping to see him play."
O'Sullivan announced in June that he had decided after refusing to sign the official players' contract, which he described as being "onerous".
The decision came a month after the 36-year-old accused World Snooker chairman Barry Hearn of "blackmailing" players and criticised plans for a revamped 50-week, 27-event circuit.
O'Sullivan's hiatus saw him miss the first three ranking events of the season - won by Ricky Walden (Wuxi Classic), Barry Hawkins (Australia Open) and John Higgins (Shanghai Masters) - and slip to number 17 in the world rankings.
He returned to non-ranking action in early September, losing in the first round of a Players Tour Championship event in Gloucester to world number 84 Simon Bedford.
He has since played six 'Snooker Legends' exhibition matches against Jimmy White around the British Isles, concluding with O'Sullivan beating the four-time world finalist 5-4 in front of 1,300 fans in Liverpool on Thursday night to level the series at 3-3.
White, speaking before news of O'Sullivan's withdrawal, had told BBC Sport he "couldn't see anyone stopping him winning in China".
"He is in good form," continued White. "He is playing well, practising hard. He was up for it.
"Ron was going to bed early every night and getting ready for his training the next day. He was looking in fine shape.
"I thought this little tour did him the world of good. It was a bit of match practice in front of good-size crowds."
Nevertheless, White - who competes in the World Senior Championships this weekend - believes people should respect O'Sullivan's stance if he decides to step away from the snooker limelight.
"I don't think there is any problem with his game. He is just a phenomenon," said White.
"I played well in our matches but one night Ronnie was 4-0 up, knocked in three centuries on the trot, it was just perfection.
"But when Ron says he finds it hard, and doesn't want to do it, it is his life, you know. I have been doing this myself for 30 years and there have been times when I didn't want to play.
"If he doesn't want to play, maybe he should have a year off. He has enough ranking points to do that."
The International Championship is the fourth of 10 full ranking events this season.
Many of the world's leading players will still take part in the event, including the world's top three-ranked players - Mark Selby, Judd Trump and Higgins.
The next ranking tournament is the UK Championship, the second biggest in the sport, in York starting on 1 December. O'Sullivan has won the UK on four occasions, most recently in 2007.