She told Sunday People that it is "hugely stressful" to play the part, which wasn't helped by the amount of money involved - "and a lot of that tension was on Daniel".
Caterina Murino in Casino Royale. Photo / Supplied
She said: "I can understand why Daniel would not want to return."
"It's not easy to go back time and time again. It can be tiring to keep trying to find new things in the same role ... It's a very tiring movie. And Daniel is not just an actor, he's a human being too."
She said when he started, Craig was "not completely relaxed" on set, and struggled with media criticism.
"People were expecting him to fail and you could feel the tension. It wasn't just a challenge for Daniel, but for everyone making Casino Royale," Murino said.
"I could tell he had a small amount of doubt about his abilities at the beginning, but he also knew the role would change his life and he would go down in history. He was happy - but frightened, because everybody was looking at him. That was a lot to carry."
