I would only encourage him. My words might be something like, "hey lad, you know you've come a long way, right?. There were plenty of you in the academy but we picked you because we know of your capabilities. You're grown now and fit to play in the league. Just give them your best, give the team your best. Do what you do best, alright? You gotta show them why we brought you here ok? Good luck lad, don't let me down, you!"
:-)