George Clooney is planning to pull another ''downright dirty'' prank on Tina Fey and Amy Poehler.

'The Monuments Men' star is eager to get back at the comediennes for jokingly describing the movie 'Gravity,' in which he stars alongside Sandra Bullock, as ''the story of how George Clooney would rather float away into space and die than spend one more minute with a woman his own age,'' when they hosted the Golden Globe Awards in Los Angeles last month.

The 52-year-old star actor, who already forged an angry letter from his co-star Matt Damon, without his knowledge, and sent it to Tina, is planning something much bigger as the former '30 Rock' star urged him to ''step it the f**k up'' but isn't sure he has the guts to pull it off.

He told 'Entertainment Weekly Radio' on Sirius XM in a new interview that will air on Friday (07.02.14): ''[They] said step it up. That's the appetizer and what's coming now, the main course, is pretty brutal.''

He added: ''This one is one that I have it in my hotel room set -- taking pictures and stuff -- I'm sitting there like, 'If I do this, this is downright dirty.' I have to think if I'm actually going to do it or not.''

Matt, 43, revealed during an interview on 'The Late Show with David Letterman' on Wednesday (05.02.14) that he only found out about George's prank letter when he received an apology letter from Tina and Amy with two fruit baskets.