Oleksandr Usyk's reign as undisputed champion may last only two weeks

The IBF's long-time mandatory challenger is unbeaten Croatian Filip Hrgovic (31), who is scheduled to fight Britain's Daniel Dubois (26) on June 1st in Riyadh.

That bout could become an IBF title fight if the US-based body follows past form, with the winner tipped to then go up against Britain's former champion Anthony Joshua later in the year.

The IBF stripped Fury in December 2015, 10 days after the Briton took that title along with the WBA, WBO and IBO belts from Ukrainian Wladimir Klitschko.

Then, as now, there was a rematch clause that ruled out a title fight with the IBF's then-mandatory challenger Vyacheslav Glazkov.

Reuters contacted the IBF for a comment, without immediate response.

Usyk - now the WBA, WBC, IBF and WBO champion - said in the ring after his split-decision over Fury that the rematch was on and Fury made clear he was expecting it.

"I'll be back. I've got a rematch clause," said the previously undefeated Briton, who had held the WBC title.

His promoter Frank Warren added that it was Fury's decision to make.

"That's what the contract says. It's what he wants. It's his call, it's Tyson's call. So whatever he wants to do, it's up to him," Warren said.

The fight in the early hours of Sunday morning unified the major heavyweight titles for the first time since Lennox Lewis last held them in 2000.

Lewis was WBC, WBA, IBF and IBO champion until the WBA stripped him of its belt because he chose not to fight a mandatory challenger. The IBF took away its belt in 2002 for similar reasons.

"The #FuryUsyk winner will be undisputed (have the four belts) for less than two weeks," leading U.S. boxing journalist Dan Rafael told his 287,000 followers on X.

"Winner will, by contract, vacate the IBF title which will be contested by overdue mandatory Hrgovic and Dubois on June 1. A 25-yr wait to get 2 weeks of another undisputed heavyweight champ."