Matt Damon turned down $250 million to play the lead in Avatar, he reveals to British GQ in their latest cover story. 

"Jim Cameron offered me Avatar," he tells the magazine. "And when he offered it to me, he goes, 'Now, listen. I don't need anybody. I don't need a name for this, a named actor. If you don't take this, I'm gonna find an unknown actor and give it to him, because the movie doesn't really need you. But if you take the part, I'll give you 10 percent of…'"

According to GQ, that would have added up to $250 million. The role eventually went to Sam Worthington

And yes, he does admit that he regrets passing on the role, which has four sequels in the works. 

"So, yeah. I've left more money on the table than any actor, actually," he admits. "I mean, the bigger thing still to this day, my bigger regret is — it would have caused a problem for Paul Greengrass and for all my friends on The Bourne Ultimatum, so I couldn't do it — but Cameron said to me in the course of that conversation, 'Well, you know, I've only made six movies.' I didn't realize that." 

He continued: "He works so infrequently, but his movies, you know all of them. So it feels like he's made more than he has. I realized in having to say no that I was probably passing on the chance to ever work with him. So that sucked and that's still brutal. But my kids are all eating. I'm doing OK."

Damon can next be seen in Le Mans ’66, co-starring Christian Bale.