The actor insisted on doing his own stunts for the tense spy drama, for which he gained weight and grew a beard, and one fight scene left him in crippling agony.
As he recovered in hospital after the movie wrapped he admits he thought about ending his life - because the pain was too great.
He tells Rolling Stone magazine, "I was at a point where I thought, 'I can’t exist like this. I can’t actually live.'
"I was lying in a hospital bed with an IV (intravenous drip) in my arm, unable to move, having these headaches where it feels like you’re having a stroke, and, for a short three-week period, I started to think, 'I may have to do something drastic about this'.
"You start to think in terms of, you don’t want to leave a mess, so go in the garage, go in the car, start the engine. It seems like the nicest way to do it."
All the pain was rewarded at the Oscars the following year - Clooney won a Best Supporting Actor Academy Award for the role of Bob Barnes.