Michael Cera thinks 'Scott Pilgrim vs. The World' is "tricky" to market.

The 22-year-old actor - who plays the geeky title character in the action comedy - admits he is not surprised 'The Expendables' beat them at the US box office because it is an obvious choice for cinema goers.

He said: "It's an easy choice - seeing the wrestler Stone Cold getting punched by Stallone or. Gosh, it's like saying, 'Would you like pizza or would you like this beautifully prepared spaghetti dish that this fine chef made?

"I think 'Scott Pilgrim' is a tricky one to sell. I don't know how you convey that movie in a marketing campaign. I can see it being something that people are slow to discover."

The Canadian-born star also admits he would like to try his hand at more writing, something he already tried with his 2006 web series 'Clark and Michael'.

He revealed to Time Out London: "If it happens, I'd love to. I love writing with friends, even if it comes to nothing. Someday, maybe when I've got a bit more experience, I could do it."