Heavyweight world champion Tyson Fury pulled out of his rematch with former champion Wladimir Klitschko on Friday because Fury is "medically unfit to fight," his promoter said.
The fight had been scheduled for Oct. 29 in Fury's hometown of Manchester, England.
Multiple sources with knowledge of the correspondence between Fury's camp and Klitschko's camp on Friday said it included a letter from Fury's doctor. The letter said Fury had mental health issues and would be "unavailable for the foreseeable future."
Mick Hennessy, Fury's promoter, released a statement Friday afternoon, but he did not divulge Fury's medical issue.
"It is with the deepest regret that we have to announce that the world heavyweight championship rematch between Tyson Fury and Wladimir Klitschko will not be going ahead," Hennessy said. "Tyson has, this week, been declared medically unfit to fight. Medical specialists have advised that the condition is too severe to allow him to participate in the rematch and that he will require treatment before going back into the ring.
"Tyson will now immediately undergo the treatment he needs to make a full recovery. We and Tyson wish to express our sincerest apologies to all those concerned with the event and all the boxing fans who had been looking forward to the rematch. Tyson is understandably devastated by the development.
"We will be making a further statement in due course. Until then, we ask that Tyson and his family be given the privacy and the space he needs to recover during this difficult time."
Klitschko had been training in his native Ukraine and was planning to head to the mountains in Austria for the rest of his camp Tuesday before word came Friday morning that Fury had pulled out of the fight.
After being informed of Fury's withdrawal, Klitschko's attorney, John Hornewer, wrote a letter to various sanctioning bodies. In the letter, obtained by ESPN.com, he wrote, "Earlier today, the Klitschko camp was informed by the Fury side that Tyson Fury will not be fit to participate. ... On behalf of Mr. Klitschko and K2 Promotions, LLC, this office respectfully requests that the organizations make the appropriate inquiries of Mr. Fury as per your rules and regulations and that you keep the Klitschko camp informed of your progress and decisions related to this matter.
"Please permit this to confirm that Mr. Klitschko remains ready, willing and able to box and will await word on next steps."
It is the second time the rematch was erased from a planned date. The fight was originally scheduled for July 9, also at Manchester Arena, but Fury pulled out in late June after he said he sprained his ankle during a training run and his doctor told him he needed to lay off it for about six weeks.
When the fight was rescheduled earlier this month, the camps scheduled a news conference for Sept. 5 in London, but it was called off the day before. It was rescheduled for Sept. 12, also in London, and while the promoters and Klitschko, 40, showed up, Fury, 28, skipped it. He said his car broke down.
"Wladimir is totally disappointed that the guy postponed again," Bernd Boente, Klitschko's manager, told ESPN.com. "Wladimir is being held hostage by this guy. He wants to fight, he trains, and now the first fight is almost a year ago. It's up to the governing bodies to make a decision regarding the titles, but that is not in our hands. We hope Wladimir can fight again soon."
Last Nov. 28, at ESPRIT Arena in Dusseldorf, Germany, where Klitschko (64-4, 54 KOs) is a major star, Fury (25-0, 18 KOs) pulled off one of the biggest upsets in heavyweight history. He ended Klitschko's 9½-year title reign by unanimous decision (116-111, 115-112, 115-112) to claim his various sanctioning-organization title belts and the lineal world championship.
Fury was later stripped of one of the belts for failing to fight a mandatory opponent because Klitschko exercised his right to an immediate rematch, as spelled out in their contract in the event he lost.
The latest withdrawal could lead other organizations to strip Fury for inactivity.
Fury tested positive for the banned steroid nandrolone in an earlier fight, even though, for reasons that are unclear, the results did not come to light until June, well after he had beaten Klitschko.
Fury, who denied taking a banned substance, faces a Nov. 4 hearing, and if found guilty, he could be banned. Testing for the rematch was being overseen by the Voluntary Anti-Doping Association. According to sources with knowledge of the testing, Fury already has been tested twice, but no results have been disclosed yet.