The 37-year-old actor said he had to have a pause for thought before agreeing to play the role, reported Contactmusic.
"My reservation was 'Well, this is a very iconic character, there will be a lot of attention on it. This was before I had had any significant success [but] I knew there would still be a lot of focus on it.
"And while I had done work, it wasn't stepping into the populist limelight like playing a character like Holmes. So I did have a pause for thought," he said.