Talks came to an impasse in October, however, after Khan remained insistent on a rehydration clause, which would mean the naturally-bigger Brook would not be able to put on more than 10lb from the weigh-in to the fight night.
The pair are working together once again as Hearn targets a date in the spring, but a fight against Crawford could threaten those plans.
Khan told Express Sport: “The Kell Brook fight is always going to be there – he’s not going to go anywhere.
“If I don’t fight Crawford, Crawford won’t be there again. That pound-for-pound title might not be there again. The world title might not be there again.”
Hearn has delivered some harsh news for his fighter, however, telling iFL TV: “I think [Khan] thinks that if he was to lose to Crawford, that he could fight Kell Brook.
“Let me make one thing clear, that ain’t happening. If he don’t fight Kell Brook next – that fight will never happen.
“And it will never be the fight that it is now. If Amir was to lose to Crawford, or Kell was to lose in a big fight, it’s not the same.”
Hearn has not minced his words to Khan, either, saying: “I’ve said to Amir: ‘Don’t think that the Kell fight is there after Crawford, because it won’t be.’
“Because Kell is going to dive into a monster fight himself, and it’s too dangerous at that elite level to presume everything is going to be OK.”
Saturday’s fight at Sheffield Arena is a final eliminator for Jarret Hurd’s IBF and WBA super welterweight world titles, and Brook has plans of his own, Hearn said.
“It’s a big night for Kell, I think he looks great,” Hearn continued.
“He’s probably weighing about 153lb today, so he could probably make 147lb if he wanted to. And he just has that fire in his belly again.
“Everyone is talking about the Khan fight, but he wants any of those big fights at 147lb or 154lb.
“He’s talking about Shawn Porter, he’s talking about Errol Spence Jr, he’s talking about fights at 154lb.”