Anthony Joshua

Anthony Joshua v Oleksandr Usyk confirmed for Tottenham on 25 September

Joshua, 31, will risk his IBF, WBA and WBO belts against the Ukrainian, who is his mandatory challenger.

Usyk, 34, has not fought for a title as a heavyweight but held all four belts a division lower at cruiserweight.

Joshua was ordered to defend his WBO title after the collapse of his bout with fellow Briton Tyson Fury.

"We are two Olympic gold medallists who have fought our way to the top and never avoided challenges," Joshua said.

Anthony Joshua v Tyson Fury might not happen until 2023, fears Steve Bunce

The all-British fight had looked set to take place in Saudi Arabia in August.

But it fell through when Deontay Wilder's team won an arbitration hearing stating the American had a right to a third fight with Fury.

"It might not be December or even next year," said Bunce.

The much anticipated fight between Fury and Joshua would have seen the pair contest all four world titles for the first time in the sport's history.

Fury is the WBC champion while Joshua has the WBO, WBA and IBF belts.

Joshua looking for Plan B after Fury fight thrown into doubt

Britons Fury, 32, and Joshua, 31, had agreed to a heavyweight title bout in Saudi Arabia on 14 August.

But earlier this week a US judge ruled Fury must fight American Deontay Wilder for a third time by 15 September.

Hearn, Joshua's promoter, said the "game changed" with the ruling.

"We have to have a plan B in place. The one that springs to mind is the WBO mandatory - Oleksandr Usyk."

Less than a week ago Hearn told BBC he did not have any back-up plan in place because he was confident Joshua-Fury would be finalised.

Fury-Joshua bout confirmed

Joshua, 31, holds the IBF, WBO, WBA and IBO titles while Fury, 32, is the WBC belt holder.

"August the seventh, August the 14th. I think it's a very bad secret that the fight is happening in Saudi Arabia," Eddie Hearn, head of Matchroom Sport and Joshua's promoter said.

Joshua won back his belts from Andy Ruiz Jr in Diriyah, on the outskirts of the Saudi capital Riyadh, in December 2019. He had lost the belts to the Mexican-American in an earlier shock defeat.

Hearn said Fury's lawyers were going through the fine details but an announcement could come this week.

Outrage as Saudi Arabia emerges as favourite to host Anthony Joshua v Tyson Fury fight

The pair could also share about £95 million (NZ$183.6 million) in pay-per-view fees in a potential split with four major broadcasters as part of the biggest deal in British boxing history.

Saudi Arabia's main challengers are Shanghai and Singapore as promoters race to find a site after two-fight contracts to unify the world heavyweight titles were signed.

Logistical headaches of hiring and selling tickets for a 90,000 venue during the pandemic has all but ended hopes of the first fight taking place in London or Las Vegas.

Fury and Joshua to fight

Joshua beat Bulgarian Kubrat Pulev in December to retain his IBF, WBO and WBA titles and set up the prospect of a mouth-watering clash with fellow Briton Fury, the WBC belt holder.

Fury, 32, has not fought for over a year since his knockout win against American Deontay Wilder, but said last month he would fight twice this year.

ESPN reported that both fights are set to take place in 2021 with the first in June or July followed by the rematch in November or December.

Joshua and Fury may give up world titles

The all-British heavyweight showdown would be the first fight in history in which all four heavyweight titles are on the line.

Fury, 32, is WBC champion while Joshua, 31, holds the IBF, WBA and WBO belts.

"We have a fight on our hands, and sorry to the governing bodies, that eclipses all belts," promotoer Eddie Hearn said.

"We've just got to be a bit careful because you may be on the verge of saying, 'Let's just get rid of politics right now. Let's just drop all the belts because if we lose one belt, we might as well lose them all,' he told Matchroom Boxing.

Sporting his Christmas jumper, Tyson Fury has a foul-mouthed rant at Anthony Joshua

Fury, seldom short of a word or an opportunity to promote his clothing range, unleashed a tirade against Joshua, who knocked out challenger Kubrat Pulev, of Bulgaria, in the ninth round on Saturday night (Sunday NZT) at Wembley Arena.

Joshua was initially reluctant to mention a fight against Fury for the undisputed heavyweight crown in his post-bout interview, asking instead for the crowd for their opinion. Under further questioning on Sky Sport UK, he said “Whoever has the belt I would love to compete with them. If that is Tyson Fury, let it be Tyson Fury.’’

Anthony Joshua retains world heavyweight titles with KO of Kubrat Pulev

Joshua had already knocked down the plucky but one-dimensional Pulev three times – twice in the third round – when he unleashed a right hook that sent the 39-year-old Bulgarian to the canvas once again.

This time, Pulev couldn't get up and Joshua raised his right fist in the air.

Anthony Joshua defending titles against Kubrat Pulev with Tyson Fury fight on horizon

The WBA, IBF and WBO belts are back in his possession. An agreement in principle has been reached with Tyson Fury, the WBC champion, for a two-fight deal in 2021 to unify the titles in an all-British blockbuster.

Nothing is ever straightforward in boxing – especially when arranging what would be one of the biggest fights in a generation, perhaps the biggest ever in Britain – but it appears there's one major obstacle in the way of an eagerly awaited Joshua-Fury bout next year.

Kubrat Pulev.