Joe Calzaghe's WBO super-middleweight defence against Brian Magee in Belfast on Friday has been cancelled.
Calzaghe has fallen foul of more contractual wrangling
The WBO has stopped the fight because of a rule which prohibits a champion from fighting less than 60 days before an enforced mandatory defence.
Calzaghe was last month ordered to fight number one contender Mario Veit in Germany on 7 May.
Veit's promoters protested over the Welshman's match against Magee, and the WBO has accepted their complaint.
Eamonn Magee will now top the King's Hall bill in his WBU welterweight title fight against Allan Vester.
Calzaghe's promoter Frank Warren told BBC Sport he had been led to believe that Veit's promoters were happy for Friday's fight to go ahead because the bout in Germany would be re-scheduled for June.
"But late last night I got a fax from [Veit promoters] saying that ZDF, the German broadcaster, were refusing Joe to fight in the interim because they had no other date other than 7 May for the Veit fight," said Warren.
"I'm annoyed but more importantly Joe, Brian Magee, the supporters were expecting a great fight.
"Joe's trained very hard for the fight and for once there were no injuries, and now this happens at the last minute.
"I'm obviously unhappy and I've got my doubts the Veit fight will even take place on 7 May because I don't know how financially they can make it work in Germany.
"They have no British TV - there's no Sky date available on the 7 - and I don't know how they're going to make it work."
Warren admitted the cancellation was another unwelcome set-back for Calzaghe, whose career has stumbled over the past two years because of injury and contractual problems.
"In the short-term, it's not good for him," Warren added. "He needed to get back in the ring and I thought Magee was an ideal opponent for him.
"I thought he would beat Magee and it would have been what he needed.
"The fact he was going into the guys back yard was the right mental challenge for him. But that's now all out the window."
Magee's trainer Pat Magee said his fighter was "devastated" by the late cancellation.
"As far as I know the Germans have objected to Joe putting his title on the line," said Magee.
"We are hopeful of sorting out some kind of substitute fight for Brian but it is very late notice for that.
"It is a nightmare for everybody concerned and I have to protect Brian's position because all this is no fault of ours."
All the other scheduled fights on Friday night's undercard will go ahead as planned at Belfast's King's Hall.
Ticket holders have been given the choice of attending the event or claiming a full refund.