An agreement is already in place for a third fight between Tyson Fury and American Deontay Wilder, according to the Briton's promoter Frank Warren.
WBC heavyweight champion Wilder and Fury are preparing for a rematch in Las Vegas on Saturday after their initial bout ended in a controversial draw.
Warren says a trilogy clause is in the contract.
"The loser has 30 days to call on the rematch and that has to be accepted," he told BBC Radio 5 Live.
Fury, 31, hit the canvas twice but believed he had won their enthralling December 2018 fight in Los Angeles.
The man nicknamed 'the Gypsy King' looked destined for an honourable loss after out-boxing Wilder, 34, for much of the fight before being floored by a savage combination in the final round.
But Fury - who spent three years out of the ring due to mental health issues after defeating Wladimir Klitschko in 2015 to claim the WBA, IBF and WBO heavyweight titles - crowned a remarkable return to the world stage by clawing himself back to his feet to make it to the final bell.
The judges could not split the pair - scoring the fight 115-111 for Wilder, 114-112 for Fury and 113-113 - and the controversy surrounding the decision added further spice to this weekend's rematch.
"This is probably the most anticipated heavyweight title fight in the last 20 years," said Warren. "It's a fantastic fight. A big puncher versus a consummate boxer. It's a bit like Muhammad Ali v George Foreman years ago - similar styles.
"What's important about this fight is that they are both at the top of their game. It's not like the young guy fighting the old guy, passing on the baton. These guys are at the top of their game and it doesn't get any better than this if you are a boxing fan."
