Joshua, 32, lost for the second time in his career but remains one of the most popular faces in the sport.
The British superstar could become a three-time heavyweight champion of the world but knows he has a mountain to climb against the Ukrainian in this summer’s rematch in Saudi Arabia.
A former undisputed cruiserweight champion, Usyk has made the step up to heavyweight look relatively easy.
And the Olympic gold medallist claimed his 19th career win at the Tottenham Hotspur Stadium by defeating Joshua by unanimous decision last September.
That saw Usyk become just the third boxer in history to become cruiserweight and heavyweight world champion.
And Haye – who counts himself one of those lucky three – believes Joshua could retire if he loses in his rematch despite suggesting he has got what it takes to win the fight, a claim both Eddie Hearn and Joe Markowski will no doubt hope is hyperbole.
Haye told The Sun: “If he doesn’t win, I am not sure he wants to be in a sport where he knows he is not the best.
“He got out-hustled by someone he knows he can beat and if – he does everything right and Usyk still beats him – I don’t know if there is anything else for him to do in the sport.
“He is such a winner that I don’t know what he does next, if he loses again.
“He believes he has all the physical abilities to beat Usyk, so do I, so with the right plan he can get the victory.
“I think his performance this time around can’t be worst than in the first fight.
“In terms of tactics and gameplan, that was the worst, so I am sure Robert Garcia won’t do that again.
“Change is good; different methods face and voice.
“In the first fight, whoever was saying what and whoever came up with the plan is irrelevant, he just has to win this fight to get back on top of the world.”
It comes after Hearn claimed that a victory for AJ could set up a domestic clash with Tyson Fury later this year.
Speaking on talkSPORT, he said: “I think the fight between AJ and Fury is always there.
“I mean, I still get questions walking down the street, even today, ‘When’s AJ fighting Fury?’
“It’s like, ‘He’s got Usyk first’. ‘Oh, has he?’ So of course, you don’t want to go back-to-back defeats but Usyk is also pound-for-pound, I think possibly no.1 right now.
“Losing to Usyk is never terrible, the Fury fight is always there, but for the undisputed heavyweight world championship, which it would be, it would just be the biggest fight of all time.
“And I think if AJ beats Usyk, that would be an automatic fight that you will see in December.”