The 36-year-old actor, whose last film was The Fighter, explained that there was no need for him to get a haircut if he wasn't starring in anything, so he didn't bother.
"This is unemployment, this is all this is," he joked to Access Hollywood. "I haven't worked since The Fighter, and it's nice to just not bother cutting your hair.
When you're not in a job that everything always has to be, you know, worked out for a character, I just sort of let it all hang out."
But he has already got an appointment with the hairdresser booked for when he starts work on new movie The 13 Women Of Nanjing next month.