But for his costar in the upcoming thriller The American, there was no such trepidation – on her part, at least.
"He confessed … that he didn't do lots of sex scenes," Violante Placido, who plays prostitute Clara and Clooney's love interest in the film, tells PEOPLE. "I felt like this was in a way something new to him, he wasn't that experienced."
She says the relatively graphic love scene came together well, though, once they agreed to trust each other.
"We had to find a way to make it natural and let your body speak somehow," Placido says. "We were very open to one another to try and make it work. We just said 'let’s trust each other' and we did. I felt like we had to let ourselves go."
Ultimately, she says, the scene was an important one to get right.
"It had to look real; it is the turning point for the two characters," she says. "I can tell you that watching it, I don't feel as calm as I did when I was on set filming it. Just watching it is a little like … wow."
In the film, Clooney plays Jack, a professional killer attempting to escape his trade after one last assignment to the Italian countryside. The movie hits theaters Sept. 1.
Reporting by MONIQUE JESSEN