Former undisputed heavyweight world champion Evander Holyfield has urged Deontay Wilder and Anthony Joshua to fight “while the money’s there”.
Wilder again called out Joshua after defending his WBC world heavyweight title against Luis Ortiz on Saturday.
WBA and IBF champion Joshua faces WBO title holder Joseph Parker on March 31, but Holyfield warns it will be close.
“I don’t know if Joshua is going to beat Parker,” he said. “Parker’s a great fighter with a good mindset.”
Holyfield, 55, was ringside as Wilder made the seventh defence of his WBC title in New York, the American stopping Ortiz in the 10th round.
Britain’s Joshua, 28, will meet 26-year-old New Zealander Parker at Cardiff’s Principality Stadium and the winner will hold three of the four recognised heavyweight titles.
Wilder, 32, holds the other, prompting anticipation he could face the winner to produce the first heavyweight to hold all four belts.
“All three of them have got the mindset and all three are youngish too,” Holyfield told BBC Sport.
“If Joshua wins [against Parker], I think he and Wilder can both make about $250 million [£180 million] so why not make the money while the money’s there?
“In being a great fighter you make money because you have proven to the people you are the best out there.”
Holyfield was an undisputed champion at cruiserweight before becoming the only man to achieve the same feat at heavyweight.
He expects Wilder to grow in confidence after recovering from an onslaught by Ortiz in the seventh round and feels self belief will be key if Wilder meets Joshua.
“Your confidence gets even bigger,” Holyfield added. “When I beat George Foreman, I didn’t think a person with two hands could beat me. It didn’t matter how big or small they were.
“The guy with the most confidence, they get their hands off first. Somehow they figure things out because when you have confidence, you have no fear, so they take chances whether they win or lose. A person who doesn’t take chances loses.”
