Just say it?

i think he should tell her what he feels. there are sayings that 'at the blink of an eye an opportunity might be lost and regrets can last a lifetime' its really really really hard to tell your true feelings for the person you love but in case you tell her and she avoided you at least you know to yourself that you wont regret it. because he grab the opportunity to tell her what he felt. [hope your guy friend will not be busted! goodluck!]

Some girls feel irritated when their best guy pal tells them that he love her. And some girls don't. Maybe he could talk to a mutual friend and that friend will drop some hints with the girl. Just see how she reacts. If she reacts in a positive way then no problem. If negative, then there should be a plan on how he would go about professing his love to her. Or maybe not going through with it. The choice is always up to him.