Censor.NET reports citing BBC.
Promoters did not disclose details but said "the condition is too severe to allow him to participate".
"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," Tyson's promoters said.
Fury beat Klitschko on points decision on Nov. 28. The original rematch, scheduled for 9 July at Manchester Arena, was postponed in June after Fury injured his ankle.The rearranged rematch - with the WBA and WBO belts on the line - had been scheduled for Oct. 29.