How should I tell my guy friend that the girl is using him?

I have a guy friend and we have known each since we are young. I do understand that we have almost the same attitude towards loving someone. However, this past few days I found out that the girl he was trying to court is just using to cover her sadness. I believe he's knows this but he's trying to get still. But as a friend, I don't want my friend to be hurt in the end because I feel that when he had a broke up with his past relationship. As much, I'm trying to stay away not get hurt again especially if the girl is not worthy...I don't how tell this and make him realize that he has stop what he's doing...