Renée Zellweger is dreading working with George Clooney.The actress, who is due to start filming 'Leatherheads' with George in January, has confessed she is terrified of his reputation for being a practical joker. Renée told People magazine: "I'm scared. I hear he's a terrible prankster and is really patient. He strikes when you least expect it."I'm going to be on alert, I'm never going to sleep, I'm sure of it. I'll be watching my back, George!" The Oscar-winning actress has also revealed the secret of her slim frame. Renée, 37, credits her slender frame on the short lunch breaks she had while working on new movie 'Case 39'. She said: "We got 20-minute lunch breaks, that's all. At that point, I was like, you know, forget it."And running around everywhere - that helps keep me in shape too." Earlier this week, Renée revealed she craves British food. The 'Cold Mountain' confessed at the world premiere of 'Miss Potter' in London's Leicester Square: "I understand the whole beans on toast for breakfast thing. I crave it."