Derek Chisora and Deontay Wilder are putting their careers on the line when they fight in April, says promoter Frank Warren.
Former world title challenger Chisora and hard-punching ex-WBC champion Wilder are aged 42 and 40 years old respectively.
Warren believes the loser of their April 4 heavyweight rumble will have to retire.
"It's the last chance saloon for one of them that's for sure. Well, for both of them. One of them's going to get thrown out of the saloon," Warren told Your Site. "They're not youngsters who are going to come back again.
"It's definitely one of those fights. For somebody it's going to be all over for them. At their age, they're not going to recover from that."
But conversely the victor will be in the reckoning to become the mandatory challenger for the IBF heavyweight championship held by unified titlist Oleksandr Usyk, who also has the WBC and WBA belts.
Chisora currently the highest ranked contender in the IBF's heavyweight ratings.
"The IBF, they'll be calling for Usyk to defend. Usyk's been given consent by the WBC, who's the next one in, to have a voluntary defence," Warren explained.
"After that he is supposed to fight Agit [Kabayel, who will be the WBC mandatory challenger]. So we'll see what happens with that. But the mandatories are being ordered and they're going to have to be dealt with.
"They [Wilder or Chisora] could well be that. Derek was in that [mandatory] position."
But Warren added: "The thing about all of it, what does Usyk want to do? Is he up for doing it or is looking to go a different direction?
"Usyk just wants a payday. He's stamped his mark in boxing. He's the heavyweight of the 21st century and that's where he's at."
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