The 51-year-old actor, who stars alongside the actress in the new combat film didn't tell her how heavy the costumes were before they got on set, and admits she burst into tears when she tried hers on.
Speaking to US chat show host Jimmy Kimmel, Tom said: ''I made sure I was there the first day when she tried it on and was doing her stunts. She cried.
''I was standing there, all the stunt guys left, I'm friends with her husband John, and I looked at her and was like, 'What do you say at that moment?'
''I thought, I just have to try and make her laugh, I was very serious and said, 'Don't be such a wuss', she looked at me for a second and then burst out laughing.''
Tom insists he asked if there was any way the costumes could be made lighter and claims Emily trained for three months for her stunt scenes.
He said: ''When I got it on, I thought, 'There's no way to make it any lighter'. I knew it was going to be challenging. It just looks cool on film.''