Is the pain under your knee cap or tendon? From what you are saying it sounds like your saying under your knee cap.
You could have patellofemoral syndrome; very common for cyclists (read your bio). Try this website.
Rest will not only the solution, kindly suggest, which thing make tendon powerful?
there is a high possibility that your tendons need some rest. Maybe that's why they are sore. Once a tendon become sore, it releases inflamatory chemicals for warmth and this can cause pain in the affected region. SO take rest,