The 'Glee' beauty stars alongside the heartthrob actor – who recently split from his wife of six years Demi Moore – and she has confessed she "freaked out" when she found out she would be working with him on the film because he is totally out of her "league."
Lea – who separated from Broadway actor Theo Stockman in September after a 17-month relationship - told New York Magazine: "I didn't mention Ashton's name just because, I gotta say, I kinda felt like he was a little out of my league.
"You know, this guy's like, the hottest guy, and then when they called and said that Ashton was doing it, I was really freaked out. I thought I should have picked someone else and said, 'You have to use this person!' so I wouldn't have been nervous.
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"But I'm so glad, because he challenged me, and it was a really great pairing, I think."
Ashton also enjoyed filming scenes with Lea where the pair are stuck in an elevator and found her to be great company.
He added: "I think what makes her great for this particular role is she has this passionate aspiration and I think that she's able to express that really cleanly."