Joshua's second world heavyweight title fight against Ruiz Jr. will be held in Saudi Arabia on December 7, while WBC champion Wilder announced his own rematch with Luis Ortiz in Los Angeles on November 23, Sky Sports reported.
But Hearn raised doubts about whether Wilder will finalize another WBC title defense against Fury, with a string of lucrative fights at stake following Ruiz-Joshua II.
"I don't see how the February fight with Fury can happen," Hearn told Sky Sports.
"To be honest with you, I think the whole world is looking at Joshua-Ruiz, and I don't think anything will happen until that fight takes place, because you've got Joshua, Ruiz who's with the PBC and Al Haymon, so is Deontay Wilder.
"If Ruiz beats Joshua, they'll be looking to make that fight, an undisputed fight, but obviously if Joshua wins, that throws everything out and who can rule out Joshua against Tyson Fury at Wembley next summer.
"Win or lose against Ruiz, that's a fight we must see, but the focus for AJ is just to beat Andy Ruiz.
"Wilder and those guys, their future is defined by themselves. For Joshua, it's never been about Wilder, it's been about the undisputed, but that dream is over until he gets his belts back on December 7."