The Brit was promoting the pair's new movie Burnt when she revealed she quit a theatrical venture after discovering her male co-star was earning more than she was.

She explained, "I walked away from a play that I wanted to do because I was offered less than half of what the other man was offered and it was just the two of us. I did what we (women) have to start doing, unfortunately, at the expense of our creative dreams."

Her comment came just hours after another Cooper leading lady, Jennifer Lawrence, published an article on gender inequality in Lena Dunham's feminist publication, Lenny Letter.

Asked for his thoughts on The Hunger Games star's feminist piece, in which she admonished herself for not fighting for a salary equal to that of her male castmates, including Cooper, before shooting American Hustle, the actor admitted he hadn't read it yet, but added, "One thing I could say is that's interesting because if you think that you only deserve a certain amount and that's not correct, it's about changing that mindset and sticking up for yourself the way that Sienna did. So that's a great thing."