The 'Iron Man' director says the movie's release is "inevitable" but he is unsure whether the 2012 film - about the group of Marvel comic book superheroes - will be a success or let-down.
He said: "I think that's fun. I think it's inevitable, and 'The Avengers' might be the thing that helps rescue us from the inevitable sequel slump that you get into because you're throwing everything on its ear.
"It might be a failed experiment or it might be something wonderful, but it allows you to add complexity in an organic way where you're culminating with something bigger, as opposed to trying to play out and not repeat the same story over and over again."