Joshua, a former two-time heavyweight titleholder, was knocked down an astonishing four times by Dubois before being defeated by a fifth-round knockout at Wembley in September.
After this loss, the Watford native was set for a critical rematch with Dubois on February 22. However, Hearn indicated that due to the severity of the 35-year-old's injury, that date is too soon for Joshua's comeback.
He said, “We had a very awkward call,” he told Boxing News.
“He wanted to fight on February 22 and basically was told that there is no way you can start camp and be 100 per cent for February 22 physically.
“There’s nothing major.
“There are two or three issues that he had a little bit in camp and after the fight.
“And they said you need to come back in May-June, and he didn’t want to do it.
“He wanted to fight on February 22, but unfortunately we kind of had to overrule him on this and say no because we can’t afford not to get this right.
“If you get beaten again by Daniel Dubois, you have to seriously consider your future.
“We got one last chapter in this career that we need to make sure we get a 100 per cent spot on.
“So when he comes back in May or June or whenever that’s going to be, you have to be physically mentally 100 per cent ready.
“He wants to rematch Daniel so bad.”
Hearn also mentioned that Joshua did not sustain a significant injury.
“There’s no major injury,” he added.
“Every fighter has niggles in camp, especially when you’re a heavyweight who trains every day and spars really hard.
“There’s nothing that’s going to be a long-term problem.
“For a turnaround after a five- or six-week break after a defeat like that, it’s just not possible to be a hundred per cent.
“There’s no tear in the bicep, just wear-and-tear that means he cannot go into a training camp with the same intensity that he would want to.”
A potential matchup between Joshua and Tyson Fury, who has been associated with a highly anticipated bout against the Watford-born boxer, is currently under consideration.
Prior to this, Fury is set to compete against unified champion Oleksandr Usyk on December 21, following his defeat to the Ukrainian in May.