Deontay Wilder will not accept an offer from Tyson Fury to skip a trilogy fight and allow the Brit to face Anthony Joshua .
Fury would rather take on his fellow countryman for the four heavyweight word titles - but Wilder wants an immediate rematch.
The dethroned champion has three weeks to trigger a clause in his contract which will allow him to challenge for his old title by July 18.
And that would push back a clash between Fury and Joshua until November or December.
"Right now, the clause for a third fight with Tyson Fury has not been activated yet," Wilder's manager Shelly Finkel told World Boxing News . "Deontay intends to activate it, he wants the trilogy.
"I can confirm Deontay will exercise his right to fight Tyson Fury next. That’s the fight Deontay wants. It will happen next."
Fury and his promoter Frank Warren had hopes Wilder would agree to sit out the rematch in exchange for a multi-million-pound fee.
"I prefer to go straight to Joshua but that's the contract," Warren told the BBC. "If he insists on the fight, we're locked into it.
"It has to be honoured unless we reach some accommodation for him to step aside. We could pay him to step aside if he wants to do that, but that's his choice.
"It would be lucrative for him, but I have spoken to his manager and Deontay does believe he has the beating of Tyson, and he can knock him out.
"I don't believe that. I fancied Tyson to stop him before the fight at the weekend."
The trilogy fight is contracted to take place by mid-July - likely in Las Vegas - while Joshua is due to defend his belts against Kubrat Pulev on June 20.
Assuming both Brits retain their titles, their undisputed clash could take place in Saudi Arabia before the end of the year.
