Tyson Fury has promised to beat Anthony Joshua inside six rounds of the mega-fight that "has to happen".
Joshua will first defend his IBF, WBA and WBO belts against Oleksandr Usyk on September 25, live on Sky Sports Box Office, before Fury's WBC title is on the line against Deontay Wilder on October 9.
The dream undisputed heavyweight championship fight can be revisited if they both come through unscathed, after talks to stage it this summer broke down.
Joshua told Gary Neville's The Overlap "I'll smoke that guy" but Fury has now told Neville: "AJ couldn't smoke a cigarette, never mind smoke the 'Gypsy King'.
"The difference between me and him? He's a businessman and I'm a Spartan. I'll show him that when I get in the ring.
"I will absolutely annihilate that bodybuilder.
"He wouldn't go past six rounds. It would be over quickly. He knows that and his whole team knows it."
Joshua previously said about the breakdown in negotiations to fight Fury: "I just know on my end, and my management team and my promoter - we've done everything we can to make this happen and as long as I'm champion, I'll compete with anyone."
Fury responded: "I have never been optimistic about this fight happening.
"Even when the deal was done, I was never optimistic. Guess what? It never happened.
"I do think, sooner or later, it has to happen.
"Even if we go AWOL, throw all the belts in the bin, to fight each other? I would do that. But I'm not sure he would be willing to do that."
Sky Sports Boxing schedule
Oscar Valdez vs Robson Conceicao - WBC super-featherweight title
September 25 - Sky Sports Box Office
Anthony Joshua vs Oleksandr Usyk - IBF, WBA, WBO heavyweight titles
Lawrence Okolie vs Dilan Prasovic - WBO cruiserweight title
Chris Eubank Jr vs Sven Elbir
David Avanesyan vs Liam Taylor - European welterweight title
Richard Riakpohre vs Krzysztof Twardowski
Mikael Lawal vs Steven Ward
Savannah Marshall vs Lolita Muzeya - WBO middleweight title
Hughie Fury vs Christian Hammer
Jamel Herring vs Shakur Stevenson - WBO super-featherweight title
Josh Taylor vs Jack Catterall - undisputed super-lightweight title