First and foremost his form should be evaluated. I've seen some horrible squatting on youtube clips. If it was me, I'd be hitting antioxidants hard. Vitamin C, l-carnosine esp. if he doesn't eat meat, coenzyme q10 at least 500mg a day, l-glutamine at least 2-3000mg per day, MSM, glucosamine,chondroitin 1000mg of each at least per day, castor oil packs for the knee...Those are some things I can think of. I hit the MSM and antioxidants hard for prevention of injuries. Also, I know my limits. Sometimes in competition the pressure is on to lift more than one's body can bear/capable of.