Chris Evans has revealed he had doubts about starring in Captain America - because of the commitment.

The Fantastic Four actor, who plays the titular superhero in Captain America: The First Avenger, was nervous before signing on the dotted line because of the huge impact it could have on his life.

"I would have been fine playing a superhero if it was one movie. The reason I was scared was because initially it was nine pictures, then it came down to six movies. Even six movies, that's 10 years, dude. I mean, I could be doing this until I'm 40," he told Collider.

The 30-year-old, who has also appeared in Scott Pilgrim Vs The World, stars alongside a stellar cast in Joe Johnston's forthcoming movie, including Tommy Lee Jones, Hugo Weaving, Dominic Cooper and Hayley Atwell. The film will open in cinemas on July 29.

He continued: "To make a decision, I don't know what I'll be passionate about tomorrow. What if I just don't want to do this any more? What if it gets weird or too much or I fall in love with writing or something else and I just want to do something else?

"My freedom is gone if I do this movie. You're signing something away and I guess I wasn't 100 per cent positive that the end game in my life was to be a gigantic movie star. And if you're not 100 per cent committed to that goal, making this decision is kind of scary. It's a big lifestyle change too," he added.