The 43-year-old actor is preparing himself to play Joker in the film, reported Ace Showbiz.
The 30 Seconds to Mars member who appears on the cover of Billboard's latest edition mentions in an interview to the magazine that he has been trying to gain weight for the role in the DC super-villain movie.
"Do you mind if I eat a little?" he asks. "I'm trying to gain a lot of weight. It means I have to eat every couple of hours - and I'm terrible at eating a lot."
Directed by David Ayer, 'Suicide Squad' will start production in April for August 5, 2016 release.