The poster shows Cooper's character covered in gold with his legs wide apart. The actor revealed that the man with the "huge package" is not him, reports WENN.
"It's brilliantly hideous, but it's eye catching," he joked. "There's this bloke in the poster with a really hairy chest and a huge package and that's certainly not me! But it is my head."
The Devil's Double sees Cooper play both Uday, the son of Saddam Hussein, and an Iraqi man forced to act as his double.
Cooper has been linked to the gangster John Gotti biopic Gotti: In the Shadow of My Father.
He also underwent a screentest for The Bourne Legacy in April.
Watch Digital Spy's world exclusive behind-the-scenes featurette for The Devil's Double below: