The 59 year old wanted to look the part as a desperate astronomer who had survived an apocalyptic event, but he took his weight loss plan a little too far and was rushed to the hospital with stomach pains just before filming began.
"I think I was trying too hard to lose the weight quickly and probably wasn't taking care of myself," the Oscar winner, who spent weeks recovering, tells The Mirror.
"It took a few weeks to get better and as a director, it’s not so easy because you need energy. We were out on this glacier in Finland, which made it a lot harder work. But it certainly helped with the character."
"I didn't know that the guy was 70 because I hadn't read the book when I read the screenplay," Clooney told Deadline. "I just knew that he was really sick... I was more gaunt and more drawn in."
"It was a balancing act. We had a skeleton crew, so we're carrying camera boxes ourselves. You could only do a take out in the snow (in Iceland) without goggles and I could only last for about a minute and 10 or 15 seconds before my eyelids would freeze shut. So I'd have to come back in and they had a blow dryer."
"We were sitting in a van and they would blow dry my eyelids so my eyelashes would melt. Then I'd go back out and shoot the scene again."