Anthony Joshua has been ordered to fight Oleksandr Usyk after hopes for a summer showdown with Tyson Fury faded this week. 

The WBO on Saturday sent a letter ordering the unified heavyweight titleholder to fight Usyk (18-0), the sanctioning body's mandatory challenger. 

While Joshua (24-1) holds the WBO, IBF and WBA belts, Fury (30-0-1) claimed the WBC title from the previously unbeaten Deontay Wilder (41-1-1) in their February 2020 rematch following a draw in their initial bout.

On Monday, a judge in the United States ruled that the dethroned champion had the right to face the Briton for a third time before September 15.

Two days later, the WBO sent Joshua's promoter Eddie Hearn a letter giving him 48 hours to show cause why it should not mandate a title defense against Usyk. 

On Friday, Hearn asked the body for an extension until Monday, but the WBO denied that request Saturday. 

The WBO gave the Joshua and Usyk camps 10 days to finalise an agreement for a fight, or the body will order a purse bid. 

Should that happen, the letter said, Joshua would receive 80 per cent of the minimum $1million bid and Usyk 20 per cent. 

Eddie Hearn is preparing to push on with finding an alternative opponent for Anthony Joshua if Tyson Fury's team are unable to "get their act together" by the end of the week.

Heavyweight rivals Joshua and Fury had appeared set for a huge showdown in Saudi Arabia on August 14, only for an arbitration ruling involving Deontay Wilder to potentially scupper that plan.

While Joshua holds the IBF, WBA and WBO belts, Fury claimed the WBC title from the previously unbeaten Wilder in their February 2020 rematch following a draw in their initial bout.

On Monday, a judge in the United States ruled that the dethroned champion had the right to face the Briton for a third time before September 15, casting huge doubt over the unification clash scheduled for a month earlier.

With the possibility of Fury no longer being available, Hearn is ready to look elsewhere for his fighter. Oleksandr Usyk – the mandatory challenger for Joshua's WBO strap – is a possibility, though the promoter plans to make sure he has more than one option on the table.

"I've been focused on plan A. The only fight we had in mind was Tyson Fury," Hearn said in an in-depth interview aired on the Matchroom Boxing YouTube channel on Tuesday.

"We hope that fight can still take place on August 14, but the game changed last night. We have to have a plan B in place – and possibly a plan C as well.

"We have a couple of different options. Of course, the one that springs to mind is the WBO mandatory of Oleksandr Usyk. They have been quite patient and, really, we're in a situation now where if team Fury don't get their act together by the end of this week, we will have no option but to look for an alternative fight.

"AJ wants to fight this summer, Oleksandr Usyk is the mandatory and we have two or three other options as well."

Hearn revealed how fellow promoter Bob Arum, who is part of Fury's team, had been "very bullish" over the hearing not being a potential roadblock in the way of the lucrative summer fight with Joshua.

"I think he was in complete and utter shock – and I don't think I've ever really heard him speechless," Hearn said of his conversation with Arum.

"He's been very bullish throughout this whole process that – and I know it's their business and we don't know too much about the contracts or the case – this wouldn't be a problem, this wouldn't stand in the way of an Anthony Joshua-Tyson Fury fight.

"That's quite frustrating. We've been working tirelessly to get this over the line. He was almost shell-shocked, I think. Once he'd calmed down and done what he had to do, I think the move was then to speak to the other side and see if there's a resolution.

"We can't be involved in that, we can't control that process, but as far as I understand it, Tyson Fury wants to fight Anthony Joshua and we had the deal to do so on August 14 in Saudi Arabia. I spoke to our partners in Saudi Arabia and they were not best pleased either.

"I think the conversations are ongoing, but from our point of view we have to get our own side in order and make our plans. Hopefully, they can resolve the issue and we can move forward with the August 14 fight. It's over to them."

Asked if he still remained hopeful over that August bout going ahead, Hearn replied: "I hope it does, because we've grafted away for four or five months to make this happen, and we've got a fantastic deal in place for a legacy fight for a huge amount of money.

"I hope, hope [it goes ahead], but hopeful? I don't know. Everything we were told from the get-go was that this arbitration issue wouldn't be a problem. It obviously is a problem now and we have to think on our feet, act accordingly.

"We still hope that the fight can go ahead, but that's completely out of our hands.

"We know what we want to do: we want to win the undisputed world championship and fight Tyson Fury. But, really, if his hands are tied, we have to look elsewhere."

Anthony Joshua and Tyson Fury have signed a two-fight deal to face each other for the undisputed heavyweight championship, promoter Eddie Hearn has announced.

British rivals Joshua and Fury have been in negotiations for several months to agree showdowns for the four major belts in boxing's glamour division.

Joshua (24-1, 22 KOs) holds the WBA, WBO and IBF belts, having successfully defended his title with a ninth-round stoppage of Kubrat Pulev at Wembley Arena in December.

Fury (30-0-1, 21 KOs) sensationally dethroned Deontay Wilder to claim the WBC crown in February last year but has not boxed since.

A date and venue for the initial encounter are yet to be confirmed, although Hearn – who promotes Joshua under his Matchroom Sport banner – told ESPN on Monday that both parties put pen to paper over the weekend.

"We'd like to get a site deal confirmed in the next month," Hearn said.

"The hard part is always getting everybody to put pen to paper. But this was a major effort from all parties to get this over the line.

"You had rival promoters, rival networks and rival fighters."

The hurdles to overcome in getting to this point were not inconsiderable, with Fury working under a co-promotional deal with Frank Warren and Bob Arum's Top Rank, both of whom have rival broadcasting agreements to Hearn's contracts with Sky Sports in the UK and DAZN globally.

Fury's most recent bouts have been aired by BT Sport in his homeland and via ESPN in the United States.

The expectation of ongoing coronavirus restrictions makes the prospect of at least the first fight taking place on British soil feel far-fetched, with a return of heavyweight title boxing to the Middle East – where Joshua avenged his only career defeat against Andy Ruiz Jr with a December 2019 points win in Saudi Arabia – appearing most likely.

"I actually feel we've done the hard part," Hearn said. "Speaking for myself, Anthony and his team at 258 management, I know how hard we've worked hard these last couple of months and I just feel that this fight is so big it's not a difficult sell.

"We've already had approaches from eight or nine sites. The offers have come from multiple countries in the Middle East, from Asia, eastern Europe and America.

"This is the biggest fight in boxing and one of the biggest sporting events in the world. It will be a major, major win for a country that wants to showcase itself."

Some typically idiosyncratic interviews from Fury over recent days, where he stated he had no interest in boxing in the UK again, while claiming to have stopped training in favour of "concentrating on getting me 10 pints of Stella", appeared to cast some doubt upon the Joshua fights getting over the line – especially considering the 32-year-old's previously well-documented struggles with alcohol and depression.

"You never really know with Tyson," Hearn said. "It could be mind games. He could be having a bad day. He could be a little p***** off. Or he could be having a joke.

"One of the fascinations about this fight will be the build-up because they're two totally different characters, two totally different personalities. The mind games will be on another level for this fight. Tyson is very good at that.

"Anthony is excited by that. He's so pumped, so focused, he hasn't stopped training since the Pulev fight. He's like a caged lion. The build-up is going to be epic."