Weightlifting Hall of Famer and five times world champion Precious McKenzie says the New Zealanders behind the project have bound him to a watertight contract and then taken too long to make the film.
"To me, it's like they're spitting in my face," he says.
Kiwi film-makers Lance and James Morcan say they're optimistic they can resolve McKenzie's concerns and that he will eventually support the $10 million movie, starring Kim Basinger and Nick Nolte.
American actor and stand-up comic Kevin Hart, 31, has been cast to play the weightlifter.
"We recognised his was a wonderful story," Lance Morcan says. "Most people in the world don't know his story."
After more than a decade in development, The Impossible Dream should begin filming in South Africa at the end of the year, Morcan says.
But McKenzie says the same promises have been made before. He regrets signing a contract with the Morcans, because it prevents him telling his story to anyone else for the next decade.
"I'm 75 years old now. I can't wait for a film to be made when I'm 86 years old."
He said the contract was presented to him while his lawyer, Alex Witten-Hannah, was on holiday. "It is a contract that is binding despite it being very one-sided against Precious," Witten-Hannah says.
"Precious would be happy if they were to come up with the money and the stars because they haven't been able to do it."
McKenzie says his latest chat with Morcan ended with the film-maker hanging up on him.
"He said to me ... he'd go on with this movie with me or without me. The way he snubbed me, the way he cut off the phone, that was an insult." .
But Morcan says the challenges were made clear to McKenzie from the outset.
"It's a very sad situation actually because Precious has been a long-time, almost a lifetime friend. We have been aware that he is becoming frustrated with the length of time it has taken.
"Many films made today are financed and driven from America, from Hollywood. They're not so interested in a story about a little Commonwealth athlete," he says.
Morcan blames trouble-makers for turning McKenzie against the film.
"I think it's a case of him taking advice from other parties who I ... would describe as greedy parties who sense an opportunity for themselves."