Actor Robert Downey Jr. is convinced his days as Iron Man are numbered because his body doesn't bounce back from injury like it used to.

The action buff has played the role of the Marvel Comics superhero for years, but after recently blowing out his ankle in North Carolina while filming a stunt for Iron Man 3, causing a delay in production, he's not sure how much longer he can play Tony Stark's alter-ego.

He tells GQ magazine, "It got me thinking about how big the message from your cosmic sponsor needs to be before you pick it up. How many genre movies can I do? How many follow-ups to a successful follow-up are actually fun?"

And the actor wouldn't be surprised if producers refused to renew his $50 million (£31 million) contract in favour of taking the franchise in another direction.

He adds, "Right now, I don't have a contract to do anything, and I did for the last five years. Fortunately I've been around the block enough - I'm not ill-prepared. And I love change."

But the 48 year old knows it will be hard to say goodbye to the beloved character when it's time to hang up the armour, adding, "At whatever point I'm done with this, I'm going to have a bit of a crisis, because I probably haven't even fully ingested how much I've enjoyed it, how much it's meant."