You can not have a man crush on a friend of yours. That is simply a strong friendship.
Two possible conditions for determining if you have a man crush are:
1. Badly wanting to be that man.
2. If your man crush approached your significant other and began hitting on her, you would excuse yourself and let him have her, at least temporarily.
When a heterosexual man has intense admiration for another man, to the point that it seems like sexual attraction (but it's not). This is usually a submissive-dominant relationship, since the person with the man crush will usually do or say anything to win the respect of (or a high-five from) the crushee.
Person 2: I thought Jay hated sports.
Person 1: Man crush...
Person 2: Ah, say no more.