What Causes Numbness Of The Knee?

I have numbness on the right side of my left knee. My family practice physician said it is probably left femoral cutaneous nerve syndrom. I am a healthy 56 year old femaile who exercises 6 days a week (biking and cross fit training) as well as tennis. I was wondering if this is anything to be concerned with. He said it will probably go away on its own but may take several months. I have no pain involved, only a tightness surrounding the knee.