If it was my son, I would sit down and have a heart to heart. Let him tell you what his plan is. If he asks your opinion. Give it. If you're not sure, go over pros and cons, best situation, and worst situation.
As others have pointed out, I think he has already cast his vote by his decision to not try out. Peer pressure and coach pressure has clouded his decision.
Nobody knows your situation better than you. Nobody knows your sons prospects better than you, and nobody knows your sons passion level more than you. Be honest with him when asked.