As Tyson Fury and Oleksandr Usyk reach to place themselves solely on the mantle as undisputed heavyweight champion of the four-belt era, it’s about time to rank the best heavyweights of all time.

Lennox Lewis, the most recent undisputed when he defeated Evander Holyfield by unanimous decision in 1999, has said the winner will be considered “one of the greatest,” but not the greatest when compared to someone like Lewis, who emerged from the era of the Klitscho brothers, Mike Tyson, Holyfield and others.

Lewis said in Saudi Arabia this week that his era was more “hard” than this crop of Fury, Usyk, Deontay Wilder, Anthony Joshua and company.

On Friday’s episode of ProBox TV’s “Deep Waters,” analysts Paulie Malignaggi and Chris Algieri said we’re poised to chase ourselves down a rabbit hole of historic proportions trying to solve this debate.

Muhammad Ali, George Foreman, Joe Louis, Rocky Marciano, Jack Johnson, Tyson, Holyfield, Wladimir Klitschko and many others can stake some kind of claim on the mythical title.

“Anytime you’re in the conversation of who’s the best of the era, it’s not out of the question for someone like Lennox Lewis to say (someone like Fury might be) the best of his era, but he’s not better than me,” Malignaggi said. “You’re supposed to think, ‘I’m the best of any era, it doesn’t matter which one you put me in.’ It’s always going to be a debate because we can’t mix eras.”

Algieri said there’s so many variables to consider. The Ali-era fighters went 15 rounds. But this era of fighters, with Usyk leading the way, are trained in superior methods.

“You’ve got to do a fantasy matchup, a theoretical thought experiment,” Algieri said.

Malignaggi kind of threw up his arms.

“There’s no real answer. You’re going to have an argument either way,” he said. “You wish you could see it.”

He told the tragic story of how a Russian man previously took on the argument that Mike Tyson was better than Wladimir Klitschko, only to so anger the man who favored Klitschko that the Tyson supporter was stabbed to death.

Still, they debated who was the best British heavyweight champion.

Both men have been knocked down multiple times. Fury went down against  Neven Pajkic, Steve Cunningham, Francis Ngannou and Deontay Wilder (four times) to post five wins and a draw. Lewis was flat knocked out by Oliver McCall and Hasim Rahman.

“Lennox beat every man he fought (through rematches),” Algieri argued.

“So did Fury. And Usyk,” countered Malinaggi.

At least something gets settled Saturday when unbeatens Fury and Usyk square off Saturday in Riyadh, Saudi Arabia.

After that outcome, get ready for that all-time great debate to warm up.

Just keep the knives put away.