The 'Thank You for Smoking' star - who gave birth to daughter Suri four months ago - is desperate to shed her post-baby weight to reprise her role as Rachel Dawes, Bruce Wayne's love interest in the 'Batman Begins' sequel.
A source told Australia's NW magazine: "Katie has been told to be ready for filming the new 'Batman' movie in January, which gives her plenty of time to get back in shape. But she has no intention of taking things slowly." The 27-year-old - who is engaged to 'Top Gun' actor Tom Cruise - has already hit the gym and put herself on a strict diet.
The source added: "She's already in the gym every day and is being super-strict about what she eats. She's also doing yoga and has started kickboxing."