The Hammers have been made preferred bidders by the London Legacy Development Corporation (LLDC) to become the new tenants of the stadium, a decision which did not surprise Hearn.
But Hearn says West Ham's move to Stratford would have a hugely negative impact on the O's.
And he believes there is a long way to go before the agreement is signed, sealed and delivered and insists Leyton Orient will explore every avenue before conceding defeat.
"I'm disappointed," he told Sky Sports News, "because it was our dream to move into the Olympic Stadium. This is not the best news I have ever had in my life. But I am not going to panic. There are certain questions to be asked about West Ham moving so close to us.
"I don't understand what harm there would be in a major Premier League club like West Ham and a community club like ours sharing the Olympic Stadium. It happens in France, it happens in Germany, it ticks a lot of boxes.
"And it would show that it's not just about cash. But I'm afraid in these difficult times, and with taxpayers money involved, it is all about cash. That's sad.
"We have to take stock of the situation and move on. We're up for ground-sharing. I understand West Ham's football tenancy is not necessarily exclusive.
"We're disappointed at stage one, but whose to say about stage two.
"One of the conditions of West Ham being the preferred bidder is that is cleared with the relevant football authorities. That's the key line. We believe it has not been cleared with the relevant football authorities to the satisfaction of Leyton Orient.
"Clearly if West Ham are moving to the Olympic Park, which is 750 feet away from our stadium, it's very difficult to believe that new fans in our local population will enter into any season ticket applications if they have a Premier League team on their doorstep - which wasn't there before - in a stadium that which has a capacity where they will be able to offer fabulously discounted deals.
"Ask yourself - if you were a kid in the Leyton area and West Ham were in the Olympic Stadium with spare capacity, where would you go?
"We are halfway through a dispute with the Premier League on the rules. They clearly feel they have done enough of an inquiry to grant West Ham permission. We feel they haven't."