The Mamma Mia! star takes on twice the work in the film, starring as Latif Yahia, an Iraqi man who was forced to work as a body double for Saddam Hussein's eldest son Uday, also portrayed by Cooper.
The actor learned how to fight for the role - and Cooper admits the sport is much harder than he expected.
He tells Britain's OK! TV, ""I did some boxing training - I was awful at it. I respect boxers so much.
""Boxing is unbelievably difficult - (after) two minutes I was exhausted and on the floor! I trained to make it look like I knew what I was doing but I'm sure if a professional boxer watched it they would think it was pathetic.""