Eddie Hearn has warned Deontay Wilder that Anthony Joshua is "close" to fighting Alexander Povetkin next, if he doesn't accepts their latest offer.
Hearn has been in discussions with Povetkin's World of Boxing team about a WBA mandatory challenge, despite ongoing negotiations with Wilder's representatives.
They have our offer so they have to accept it or move on. It's not a case of if you don't accept this offer the fight is dead, we will just fight Povetkin and carry on our negotiations to the next one.
Barry Hearn is currently out in New York and is expected to meet up with Shelly Finkel to see if they can come to an agreement five weeks after the 'Bronze Bomber's $50m offer for a historic unification showdown.
Joshua's promoter maintains that the British star wants Wilder next but also wants to fight in September, which would also clear up any WBA mandatory obligations.
"I don't like making deadlines because sometimes it gets people's backs up but at some stage soon we have to make a decision," said Hearn.
"We are close to closing a deal with Povetkin with (Andrey) Robinsky and World of Boxing and once the deal is closed, there is no Deontay Wilder.
"Wilder has had the latest offer from us for the last two weeks which was our improved offer and we are still talking to them and in fact, my dad is out in New York at the moment, and he might meet Shelly today.
"They have our offer so they have to accept it or move on. It's not a case of if you don't accept this offer the fight is dead, we will just fight Povetkin and carry on our negotiations to the next one.
"It has to be the next one, or the one after that. Joshua wants to fight. We've got an opportunity to go in September and Josh is keen to fight in that month and if Wilder wants it, it's there.
"But I do still believe Wilder will take this offer."
Povetkin earned the chance to challenge Joshua by knocking out David Price in their WNA final eliminator on the undercard of Joshua's success over Joseph Parker, in March.
Managers Andrey Ryanbinskiy and Vadim Kornilov have been in talks with Hearn since then and are aware that if Wilder does accept the latest offer, they are likely to face the winner.
"I've got a very good relationship with Ryanbinskiy and Vadim and I am very honest with them," Hearn said.
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"They know exactly what's happening here and they know they can't stop the Wilder fight but also, we've got a situation where they need to know what they're doing. We are talking at length on the deal and we will reach an agreement for the fight.
"It is a very, very difficult fight, the Povetkin fight. He's lost once, to Wladimir Klitschko who did everything he could to try and stop him but couldn't do it.
Whyte may have to travel
Dillian Whyte likely to fight in Bulgaria in IBF final eliminator with Kubrat Pulev, says Eddie Hearn.
"He is an extremely tough man with extremely powerful people behind him and the entire nation behind him who will desperate to beat Anthony Joshua for a world heavyweight title.
"This is a serious fight and in many ways, it's as tough as the Wilder fight.
"Josh is up for all these fights, all these tests and he is certainly up for fighting Wilder. At the end of the day, Josh could lose to Povetkin and then the Wilder fight is up in smoke."