Kell Brook branded Amir Khan a "con man" as he accused his British rival of running scared.
Brook, who faces Michael Zerafa on Saturday, shook hands with Khan last month on a fight that has been five years in the making.
But Khan looks set to renege on the deal and take on world champion Terence Crawford in March instead, leaving Brook furious.
He said: "Amir Khan is a con man, they should call him Amir Con.
"This is his last big fight under Matchroom and I thought it was nailed on. He shook my hand and looked me dead in the eye and said we would fight next. What can I do, I’ve bent over backwards and said I’d come down to 147lb.
"I’m doing everything I can for the fans, he’s turned his back on them. Everyone knows it’s him that’s running off."
Khan has been offered £4million to face Crawford in New York and has insisted the fight with Brook will "always be there".
But promoter Eddie Hearn has warned him him against that assumption.
He said: "I want the fight that’s going to create the legacy in this country, and that’s Brook against Khan. It’s a massive fight where Amir can make twice as much money as the Crawford fight.
"Amir seems to think the Brook fight is always there but it’s not. This is now or never, this is the last chance. Let’s give the British public what they want.
"If Amir can beat Kell Brook, he could fight Crawford after for more money than he’s going to get now.
"I don’t see any excuses and Kell’s right; I’ve been with him a long time and I signed Amir Khan with a view to make this fight with Kell Brook. I believe the British public deserve this fight.
"Right now I think it’s probably 50-50 whether he fights Crawford or Brook."