Joshua, 31, lost his world heavyweight titles to Usyk, 34, at Tottenham Hotspur Stadium on Saturday night. He told a post-fight press conference that he could not see anything in one eye from Round 9.
"I think he is OK. I don't think he has fractured the eye socket. That was the worry first", Hearn told reporters, after initially suggesting that his charge had suffered a bone fracture.
Joshua said this was the first time his eye was closed in a fight.
"I couldn't see in the ninth round, couldn't see anything really. The eye was shut. But it was a good experience because you just learn to control yourself, get on top of things", the boxer explained.
Joshua said he was eager to start training and promised he would be back in the ring "100%" and sparring with the Ukrainian. Hearn ruled out a rematch in Ukraine, saying it would probably be in the UK.