The 28-year-old still intends to face Wilder within the next nine months, though, and Hearn is hopeful that the latest round of negotiations with the WBC champion's camp will reach a successful conclusion in the near future.
"I'm pretty confident," he told Sky Sports News. "I think at the moment [Wilder's] throwing his toys out of the pram, and eventually we hope he'll come to his senses. I spoke to Anthony yesterday and I think what we're going to do is all the terms that were agreed by Deontay Wilder have now been put into the contract.
"They've had them now for over a month, and they haven't done anything, so I think what we're going to do, we're going to sign the contract. Anthony Joshua says let's sign the contract and put it in front of them, rather than them thinking that we're bluffing for some bizarre reason, or we don't want the fight.
"Anthony's going to have a press conference for his next fight next week and he'll be in America as well, and it will be good to go out there and say we've done all we can. You've agreed these terms, we've now even signed the contract, so fingers crossed, April 13 at Wembley will be Joshua against Wilder."