Wladimir Klitschko withdrew from his WBO and IBF heavyweight title defense against unbeaten British challenger Dereck Chisora because of a torn muscle in his back.
Klitschko's 19th title defense had been scheduled for Saturday in Mannheim, but he pulled out Wednesday with an injury described by his boxing adviser in the United States as not being particularly serious.
"Wladimir has withdrawn from the fight, that is correct. He has torn a muscle in his back," Shelley Finkel said. "It is not too serious though. He should be able to fight again within 60 days."
Frank Warren, who was promoting Chisora for the bout, told boxingscene.com that his client was shocked after hearing the news.
"Dereck is very disappointed," Warren said. "He didn't believe it. He felt everything was fine. Three or four days before a title fight, most of the hard work is done."
Talks are now expected between the fighters' representatives over rescheduling the fight.
In the buildup to the fight, the relatively inexperienced Chisora (14-0) had thanked Klitschko for the opportunity but also insulted the quality of the Ukrainian's previous opponents, his trainer and girlfriend.
Klitschko has a 55-3 record with 49 knockouts. WBA heavyweight champion David Haye wants to fight him and his brother Vitali, the WBC titleholder, in a bid to unify the heavyweight division.