Rachel McAdams was "a little scared" of Jake Gyllenhaal's ripped physique.

Rachel McAdams

Rachel McAdams

The 36-year-old actress, who is rumoured to be dating her 'Southpaw' co-star, thinks he looked like a "beast" after gaining 15 pounds of muscle to play a boxer in the upcoming movie.

She said: "I was a little scared too! He's a beast. He's a real animal. I haven't seen it yet so I can't totally comment but just watching from the sidelines he just worked so hard. I think his work is going to reflect that. It was extraordinary. He'd get up in the morning and run eight miles and then run twice a day and then rehearse. He was a machine. And I was just filing my nails pretending not to notice."

While Rachel has been romantically linked to Jake, 34, for the past few months, the actress admits she was thrilled to team up with her hunky 'Wedding Crashers' co-star Bradley Cooper, 40, again for their new film 'Aloha'.

She told E! News: "He's everything you imagine him to be and more. He's not hard on the eyes. I think he's one of the hardest working actors out there right now and he doesn't even need to be, he's got this sheer talent he could just sort of rest on his laurels but he doesn't. He works very, very hard. He's very smart and very, very committed."