Anthony Joshua has been ordered to defend his WBO heavyweight title against mandatory challenger Oleksandr Usyk after the collapse of his bout with fellow Briton Tyson Fury.
Joshua, who also holds the IBF and WBA belts, had agreed to face WBC champion Fury in Saudi Arabia.
But an arbitration hearing ruled Fury must first face Deontay Wilder.
Joshua's promoter had been given 48 hours to show why a fight with Usyk should not be mandated.
Eddie Hearn requested an extension until Monday to the "show cause" notice in order to "discuss the subject matter and other related affairs" with Joshua, but Usyk's team objected.
The WBO sided with the Ukrainian former undisputed world cruiserweight champion, who had previously agreed to step aside to allow the Joshua-Fury super fight to go ahead, and said in a statement on its website: "The extension request is hereby denied."
As a result, the two fighters and their teams have until 31 May to reach an agreement for a fight or purse bids will be called.
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