Is it his physical mannerisms? Or vocal?

If vocal, there's not much I can recommend.

If physical, pick a couple of stances, attitudes, poses, gestures - whatever you think will help - and tell him that you'd like him to incorporate them into his performance. Tell him that the others are dominating their scenes and that these few physical actions you're asking from him will help level the playing field and give him a stronger stage persona.

You can even solicit his thoughts about possible physical movements. Remember, too, that he may be holding back a little because some physical actions don't "feel" right to the actor making him reluctant to try things. He needs to know that some things that don't "feel" right actually "look" right from the audience and he shouldn't be afraid to try anything once.

In any event, don't make it about "him" - make it about the play and how to make his performance stronger in relationship to the others in the cast.

Whether he's gay or not, I'm sure he's aware that he's not really holding his own on stage; so he should willingly accept whatever you have to offer - particularly if you ask for his input as well. A collaborative effort will always work best.

A secondary approach you might use is to tell your actor you'd like him to act a little more like Al Pacino, or John Wayne, or whoever - and see if he can "channel" that actor's characteristics into his own performance.

I had a Petruchio once who needed some help, and both these approaches worked really well for us.

Needless to say, this conversation should take place in private - except when something works, then praise him publicly: "I really liked the way you sat on the edge of the desk, pounded the table with your fist, leaned in and got nose-to-nose with so-and-so during the cross examination, etc., etc., etc."

Edited by edh915 - 3/04/13 at 6:52pm

I was in a somewhat similar situation as a director a few years ago and didn't handle it well. The main thing I learned was to give all directions in the positive. If you want a different mode of speech, a different interaction with another actor, a different way of moving or sitting, tell them that in as much detail as you think the actor needs. I made the mistake of characterizing the action I was getting rather than describing what I wanted.