My son was in yesterday and had an x-ray of his left knee and the doctor said he possibly has osteochondritis dissecans. He is going back on Monday for an MRI to determine if it is stable or unstable. Will this prevent him from playing baseball in the spring/summer and football in the fall.

A lot will depend on the results of the MRI and any other tests. It's too soon to tell. Ask the doctor this question, and also ask what safeguards your son can take if/when he plays.