Is there a clinic somewhere that would assess an athletes leg strength and be able to provide a program to strengthen part of the legs.
older teenage son was doing lots of athletics (3-5 days a week) and started soccer, never had an injury but in 2 months got 2 knee injuries which I seen happening, both caused by lateral turns and knees folding under him. He loves both sports so dont want him to give up and Im not looking for medical advice here, just who would you go to to look at that and get someone to say "yeah this is whats wrong, heres a program that lasts X weeks that will build up the necessary strength in knees for pivotal sports and we can reassess then"
Sports surgery clinic? a physio? a good S&C guy? a Physiologist? a gp?
A physio that specialises in running and field sports. I wouldn't bother with a GP, many wouldn't have the specialist knowledge and would likely just do a triage and then refer him to someone else. I wouldn't go near a PT or S&C coach until there's been a diagnosis by a professional and well regarded physio tbh.
Just my advice as I'm speaking from experience here but no guarantee your experience will mirror mine obviously.