Lennox Lewis says the heavyweight division risks falling into a state of "insignificance", and he expects no 'undisputed' bout in 2020.
Lewis, 54, won the WBC, WBA and IBF titles in November 1999 when he out-pointed Evander Holyfield in Las Vegas.
He remains the last heavyweight to claim the 'undisputed' tag.
"It shouldn't be another 20 years before boxing has an undisputed heavyweight champion," said Lewis in an Instagram post.
The rise in prominence of the WBO belt since Lewis reigned means that is now also required by anyone seeking the 'undisputed' tag.
Mexican-American Andy Ruiz Jr currently holds the IBF, WBA and WBO world titles, with Deontay Wilder in possession of the WBC belt.
Fighters in other weight divisions, such as Katie Taylor, Claressa Shields, Oleksandr Usyk and Terence Crawford, have won all four but many fans were left frustrated when negotiations for an 'undisputed' bout between former champion Anthony Joshua and Wilder fell through in recent years.
"British heavies have brought excitement back to the division, and just as I said before, just when the division has a pulse, we need the best fighting the best," Lewis wrote on Wednesday, 20 years to the day since he beat Holyfield.
"If this division doesn't get on that track it faces the same fate that it's been fighting to shake off... insignificance.
"In a division where it's very likely that on any given night any of the top fighters can beat each other, it seems the only way to get to undisputed is if there is no other route fighters can take but to face each other.
"In today's climate, unless the current champs win out, I don't see an undisputed fight happening, even for 2020.
"With rematch clauses, sanctioning body politics, and without just the shear will to make it happen by all involved, undisputed will remain just a dream in the minds of boxing fans around the world."
Lewis first claimed a world heavyweight title in 1993, becoming the first Briton to do so since Bob Fitzsimmons in 1897.
Joshua looked set to be positioned for a future 'undisputed' bout until he fell to a shock loss to Ruiz in June, with the pair set to rematch on 7 December in Saudi Arabia.
American Wilder defends his WBC belt against Luis Ortiz on 23 November and has raised the prospect of facing Ruiz despite having allegedly already agreed to fight Tyson Fury for a second time on 22 February.
Britain's Fury claims to be the 'lineal' world heavyweight champion having never lost the belts he won from Wladimir Klitschko in 2015 in the ring.