Iron Man star Robert Downey Jr. has revealed he was terrified about stepping into super sleuth Sherlock Holmes' shoes for Guy Ritchie's new movie because he was convinced he could never top superstar Brad Pitt's performance in the director's 2000 film Snatch.

Downey Jr. has said that he had doubts about playing Holmes in Ritchie's new adaptation because he thought he was apprehensive if he were "cool" enough to be one of the filmmaker's leading men, reports imdb.com.

"It's was a little bit daunting. You know the type of guys that have been in Ritchie's movies and you feel like they're this kind of tight-knit little band. And I remember seeing Brad Pitt in Snatch, and thinking that was so cool. And I thought, 'I'm never gonna measure up'," he said.

Downey Jr. insisted Ritchie didn't question his casting decision and instead focused on getting the job done.

"The truth is, Guy doesn't think that way. He kind of approaches everything like (it's important to) have a good atmosphere.