Agree with Alophysio, I would check ITB, but also TFL for tightness and alos his Glut Med stability.

What I meant by checking the hip and ankle was not so much looking for injuries, but assessing tightness and lack of strength which may affect the pull on the patella. e.g. He may have weak hip abductors which would cause internal rotation of the femur leading to a tight ITB causing altered pressure of the patella in its groove and therefore contributing to his problem. (hope I explained that ok)