If he does not have big events left this Fall (WWBA/Ft. Myers or Jupiter, etc.), I would say shut him down. I bet his "feel" is just fine when he picks a ball back up this winter. If he needs to get it back right away, here below is what I would do...this is "back to basics", as someone put it, and it also really simplifies things and has worked for my son. Think about this as the "macro to micro" approach, and we first heard this phrase at my son's very first college camp (turns out he is now committed to that school), and the HC who was instructing him is former MLB RHP.
After loosening up with some light long toss, and as he he works his way back in to about 90 feet or so, have him spin some 12/6 in a light, toss manner, throwing the ball with as much arch as he needs to get to where he drops it just about chest high to the catcher (or whomever he is throwing with). This gives him margin for error, is low stress (he won't be inclined to choke the ball like he might if he was on a mound, in a game or even in the pen with a coach watching) and will allow him to regain confidence in his release point and spin rate/control. This is the "macro" portion. Do this for as long as he needs to to get the feel, then slowly have him (a) work his way in closer and (b) throw the ball a little harder with tighter spin and lower target. Do this until he gets to 60 feet and can simulate his stretch motion, with the C down and he can get it in the strike zone. Even at this point, he may need to throw it with slower spin than he might aspire to. But, his confidence will build. No pressure, no stress, clear the mind, no coach watching, no batter, no harm if he air mails one or spikes one.
Let us know if it works. Anytime I see my son bouncing curves (his grip is probably too tight, I assume) in front of the catcher early during a bullpen session, I might just say "macro to micro", and it triggers this process for him. He won't necessarily go back to 90 feet, but what he will do is take something off the velo, aim for the catcher's mask for a few pitches then work his way back down after he gets the feel back.