Cindy, the treatment will depend on how severe the injury is. If he's experiencing minor discomfort, a good warm up and regular icing should do the trick. However, if he's in a lot of pain, you should probably take him to the doctor; he may need physical therapy and/or surgery.
I believe it's a form of tendinitis, so you can find some info and treatment tips here:
http://www.webmd.com/osteoarthritis/guide/arthritis-tendinitis
