Mark Ruffalo feared 'Thor: Ragnarok' would ''break'' the Marvel Cinematic Universe.

The 49-year-old actor stars as the Hulk in the money-spinning movie franchise, but he's admitted to being worried about how the Taika Waititi-directed film diverted from Marvel's usual approach to the character.

Mark - who appears alongside the likes of Chris Hemsworth, Cate Blanchett and Idris Elba in the movie - confessed: ''You know how many times I was like, are we breaking the Marvel universe? We threw everything out!

''We started all over again with this.''

The new movie is notably more humorous than the previous 'Thor' films - and Mark admitted the film represents a risk for the studio.

He told Collider: ''We threw the 'Thor' franchise out. We threw everyone's perception of Banner out. We threw everyone's perception of Hulk out. We threw everyone's perception of Thor out.''

The new film has been widely hailed by cinemagoers and Mark believes Taika deserves much of the credit for bringing his ''rebel mentality'' to the set.

The Hollywood star explained: ''We knew what we were doing and at the same time were like, 'let's just do it. And let's go for it. And let's do it in the best and the most honest and fun way that we possibly can. And Taika did that, and he wasn't afraid of that.

''To have that rebel mentality going into it ... We improvised a lot. We played. He created a space where we could just play. And we were making jokes, and he would throw a joke in, and then that would turn into another joke ... That playfulness is really appealing on the screen.''