Being a father of Chelsea doting teenage footballer myself, I can well appreciate the predicament that you are in as also how your child might feel on being told to restrict football. It is not that he has to give up football completely but certainly the advice to restrict physical activities is well meant and well intentioned. He needs to restrict the intensity of the exercise and the duration of exercise to relatively moderate levels. I would not be too dogmatic about my advice and would certainly keep in mind the actual symptoms of the child, but in general terms, he should do marginal exercise only.