Deontay Wilder will not step aside from a third fight against Tyson Fury in order to allow his opponent to face Anthony Joshua, says Bob Arum.
Arum, who promotes Fury in the US, says a rematch between the Briton and Wilder is now set to take place in Las Vegas on July 24.
It is a severe blow to the hopes of seeing a unification bout between Joshua and Fury, who were set to fight in Saudi Arabia on August 14.
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However, an arbitration hearing found this week that Wilder had a contractual right to another rematch against Fury, and that it must take place by the middle of September.
The pair were slated to fight for a third time last year, but the Covid pandemic, as well as an injury sustained by Wilder, saw Fury move on to the planned Joshua showdown.
Fury accused Wilder of demanding $20m to step aside and allow him to face Joshua - something the American's trainer Malik Scott denied - and he told The Athletic on Thursday: "I wouldn't pay him 20 grand. I'm going to crack his skull wide open this time."
And Arum told the Boxing Social: "No, there's no chance that he [Wilder] will step aside. He doesn't want to step aside, except for a totally preposterous number.
"The judge said he had a right to a rematch and we're going to go ahead with it."
Joshua's promoter Eddie Hearn said he was initially under the impression the arbitration hearing would not pose a threat to his man's chances of fighting Fury this summer.
Arum insisted he was also taken aback by the ruling, saying it was "totally unexpected and I think it was the wrong decision".
He added: "I believe that the law and the facts were on our side and that Fury could go ahead and fight Joshua. The arbitrator saw it differently.
"When you get knocked down like we did, pick yourself up, and Tyson will do that. We'll fight Wilder on July 24 in Las Vegas."
Fury's first fight with Wilder in December 2018 ended in a draw, but he stopped the 'Bronze Bomber' in their second bout 14 months later to claim the WBC title.
Discussing Fury's reaction to the news that he would have to face Wilder again, Arum said: "Tyson wasn't very happy.
"But he's going to take out his frustration and anger on Wilder, and he tells me he's going to knock Wilder out quicker this time."
Joshua - who holds the IBF, WBO and WBA heavyweight belts - labelled Fury a "fraud" on Twitter after it became clear their August meeting was in danger.
He could now face the WBO's mandatory challenger Oleksandr Usyk, who Hearn called Joshua's "plan B".
Should Joshua and Fury come through their potential fights with Usyk and Wilder unscathed, Arum is sure they will finally take each other on, saying: "Yes, absolutely.
"I don't think it's going to be difficult - if they both win - to renew talks. We know all the ins and outs and it'll come together really quickly. At least that's my hope."
Anthony Joshua could be forced to solve the sport's most bewildering mystery - how to beat Oleksandr Usyk - to save an undisputed world-title fight.
The supremely skilled southpaw has proven to be an indecipherable riddle throughout his professional career, which has led to undisputed glory at cruiserweight and 18 victories.
Usyk tinkered with a maths problem during a press conference with Derek Chisora, a boxing genius who constantly keeps the cogs whirring by completing puzzles during training sessions.
Tony Bellew admits he was left drained after attempting to outwit the Ukrainian in a knockout defeat.
"Usyk is perfect. He does everything great," Bellew told Sky Sports last year.
"He mentally exhausted me in our fight by constantly having his front foot close to mine.
"That doesn't sound much. But it's mental pressure that he puts on you, not physical.
"He wouldn't get involved in any wrestling matches with me. Every time we got close, I would dig him to the body.
"He's vicious and brilliant."