The 35-year-old actor, who is a keen enthusiast of the 1970s, was determined to authentically portray his character, reported Contactmusic.
"As my wife will attest, the Seventies is my favourite decade. I was like, 'Yes!' I love the way I look in this film.' It's the only time I've ever done that in my whole career," McAvoy said.
The Scottish actor revealed that he was left exhausted after playing four characters with psychological issues back-to-back.