What could cause pain in the outside back of the knee area when flexing the knee? Like when you do a knee dip on a serve... This isn't behind the kneecap, but near that really thick tendon near the outer side/back of the knee. It's not so much of an issue that I'll see a doctor yet, I'm just doing some resting/icing for now and that helps. Is this a typical area for tendonitis? It's not a sharp pain, it actually comes on gradually as i bend my knee, until a point where my knee feels a a little weak. It seems to come and go with use/overuse.