Baer was traveling with the actor when the incident happened.
"Gérard Depardieu wanted to go to the lavatory. He was barred access. We were not far off taking off, so he urinated in front of everyone. I passed him a small bottle," said Mr Baer, who will star alongside Depardieu in the film 'Asterix-- Rule Brittania' which is being filmed in ireland
"He couldn't wait, so I found this solution. I had a little Evian bottle with me, only it was too small so it overflowed He wanted to clear it up, but the hostess wouldn't let him," he told Europe 1 radio.
"It was naturally very embarrassing and humiliating for him. He didn't do any grand gestures and shout: 'I'm going to piss'. Whatever the larger-than-life nature of my friend Gérard, no one is that crazy."
Baer said Gerard has a prostate problem. "No one is flattered to have a dodgy prostate and be obliged to urinate. But the (hostess) panicked and said the plane must stay on the tarmac.
"I stopped him because he wanted to go and explain to the crew, he was sorry and he was furious but didn't lose his temper.
"The lady was doubtless applying the rules, but it's only human ... are you supposed to pee your pants because of security rules?"
Baer said Depardieu was "stone cold sober" when the incident occurred.