Matt Damon believes turning down a role in 'Avatar' was the "dumbest thing an actor ever did".

The 52-year-old star is thought to have missed out on a $250 million payday by rejecting the role of Jake Sully - which went to Sam Worthington - in James Cameron's 2009 sci-fi epic.

He was offered 10 per cent of the movie's box office profits if he took on the part, and by turning down the role he also missed out on the chance to team up with fellow lead actor Zoe Saldana (Neytiri).

Damon told 'Entertainment Tonight': "It’s the dumbest thing an actor ever did in the history of acting."

But Saldana told him: "I don’t think your career suffered because of it, trust me."

She joked: "I've just always felt blessed that I was picked, that I worked really hard and auditioned.

"I'm not Matt Damon. I don't get to turn down Avatars."

Damon added: "I've probably done, like, 50 movies. I've never been in a movie that made $1 billion."

In December, Cameron told Damon to "get over" turning down 'Avatar'.

Speaking to the BBC, Cameron said: "He's beating himself up over this. And I really think you know, 'Matt you're kind of like one of the biggest movie stars in the world, get over it.'

"But he had to do another 'Bourne' film which was on his runway and there was nothing we could do about that. So he had to regretfully decline."

Cameron would be happy for Damon to make a cameo appearance in a future 'Avatar' sequel but wouldn't be offering him any box office takings.

When asked about an appearance from Damon, the filmmaker said: "Must do it. We have to do it so the world is in equilibrium again. But he doesn't get 10 per cent, f*** that."