Tyson Fury vowed to knock Deontay Wilder out in the first round after signing a contract to fight the American for a third time.
The 32-year-old had looked close to finalising an all-British bout with Anthony Joshua to put all four world titles on the line in Saudi Arabia.
But Wilder's team won an arbitration hearing that the American was due another clash with Fury.
A trilogy fight with Wilder is now on the cards, with Top Rank Boxing posting a video of Fury signing for the fight in the early hours of Sunday.
Fury's latest contest with Wilder is now set for July 24, with Las Vegas' Allegiant Stadium, the 65,000-capacity home of the NFL's Raiders the likely venue.
In the video, the 30-0 fighter said: "Shall we do it and put him out of his misery?
"Crack the other side of his skull? Give him another shoulder injury, another bicep injury, a leg injury... the whole lot.
"Wilder, contract's signed, you're getting smashed. When I say smashed, I mean smash, smash, smash.
"You're getting knocked out, end of, one round, you're going, I've got your soul, your mojo, everything. I own you."
Fury first took on the then-defending WBC heavyweight champion in Los Angeles in 2018, with the Bronze Bomber retaining his strap after a controversial split decision draw.
MGM Grand Garden Arena hosted the rematch in 2020 with Fury taking the title with a seventh round TKO.
Joshua has been ordered to defend his WBO heavyweight title against mandatory challenger Oleksandr Usyk.
