What joint was involved? Knee, shoulder, ankle...? Much depends on the severity of the injury, the patient's own immune system, and the patient's dedication to rehab. One thing for certain, that joint will never be the same as it was before the injury. He will certainly have good use of it, but it's going to be painful for a good long while.
The physical therapy is the most important part of rehab. Unfortunately, it HURTS. I hope your son's doctor is making sure the pain issue is addressed so that PT will be successful. It's very important he do his homework exercises as prescribed by his therapist. I skated out of rehab after surgery on my left knee years ago, and have paid for it all these years. It's full of scar tissue and noticeably weaker than the other knee. Totally my own fault, but what did I, as an ignorant high school kid know? :-)
I'd say your son is probably on the bench for the rest of the season. Hopefully he'll keep up the rehab work and be back in uniform next year with no further trouble.
Welcome to the Pain Management Forum of MH. I'm glad you found us. Jaybay is correct, much will depend in the joint involved and the amount of damage and repair that was required.
I look at this a bit different. When will it be safe for your son to return to the field? I would want to be sure that the injury and damage that was suffered will not be a life long problem and that playing again will not subject him to a more severe injury. Indeed one that could change his life. Those "young" injuries have a way of creeping up on us as we become older. I have seen it time and time again. Don't let this happen to your son if you can help it.
Rehab by a sports injury specialist is extremely important. And yes it will be painful. Probably more painful than the injury. I wish him fast and complete healing. Please take care and let us know how he is doing. Tuck