Middleweight titleholder Sebastian Sylvester's defense against Mehdi Bouadla was postponed Monday because Sylvester "felt ill and exhausted," said Chris Meyer of Sauerland Event, Sylvester's promoter.
Germany's Sylvester (34-3-1, 16 KOs) was due to make his fourth title defense against Bouadla (21-3, 10 KOs) of France on Saturday in Neubrandenburg, Germany.
Meyer said Sylvester has seen a doctor and that they are waiting for the medical report with the diagnosis of his specific ailment. However, Meyer said the card likely will be rescheduled quickly.
"Based on the result of the examination we will reschedule the card to as early as Feb. 5 or 12," Meyer said.
Sylvester was making an optional defense and Meyer said he would need "the approval of the IBF to fight [an optional] later than Jan. 22."
The entire card has been postponed, which also means cruiserweight titleholder Steve Cunningham (23-2, 12 KOs) of Philadelphia, who is already in Germany, also will have his undercard fight against mandatory challenger Enad Licina (19-2, 10 KOs) of Serbia delayed.
Sylvester is coming off an October title defense in which he scored three knockdowns against countryman Mahir Oral en route to a lopsided decision win.
Cunningham regained the belt he once owned by stopping Canada's Troy Ross -- a former winner of "The Contender" reality series -- in the fifth round in June to win a vacant title.
Dan Rafael covers boxing for ESPN.com. Follow him on Twitter.