The 34-year-old star said that he was not much concerned about the ending of the movie based on Irvine Welsh's best selling novel, but wanted his character to be killed, reported Contactmusic.
"I love the fact that he killed himself, I wasn't worried about the ending. I was worried when people were trying to make it a happy ending, there was always talk of 'maybe he should make it', 'or people don't know if he's killed himself or not'," McAvoy said.
"I think helping to bring Irvine Welsh's abusive, beautiful, nasty and hilarious world onto screen and do it well - it's a privilege," he added.
McAvoy said he was surprised to see the response of the film, which raked in over USD 4 million at the box office.
"When it was made everyone was saying you'll make USD 2 million at the box office, and we'll do well here, but we made over twice the budget," he said.