The 34-year-old actor said his respect for boxers has skyrocketed, reported People magazine.
"The amount of time you have to put into it, the sacrifice that you put into your body, it's not something that you're eager to do again. It's a huge commitment," he said.
"One thing I know, and we always talk about, is whatever you put into your character, how much commitment you have to put into the movie, all of that energy is in the film. I can feel that energy when people see the film.