Undisputed world cruiserweight champion Oleksandr Usyk has pulled out of his heavyweight debut against Carlos Takam because of a biceps injury.
Ukrainian Usyk, 32, was due to face Takam, 38, in Maryland on 25 May before sustaining the injury in training.
Promoter Eddie Hearn said the fight had been postponed and an announcement about the show in the US state would be made shortly.
Usyk is the first boxer to hold all four world titles at cruiserweight.
The 2012 Olympic champion's final bout in the lighter division came in November when he knocked out Briton Tony Bellew - a seventh successive world title victory.
He is unbeaten in 16 professional fights, with 12 knock-out wins.
Cameroon-born Takam fought Britain's Anthony Joshua for the IBF, WBA and IBO world titles in October 2017, and took him to 10 rounds. He also battled another Briton, Derek Chisora, last July and suffered an eighth-round knockout.