Rehab a Quadricep

Has anyone out there ruptured a quad tendon before or know somebody who has? I had a piece of tendon taken from my quad about a year ago and am still having difficulty getting my quad back to size. I figured since bodybuilders rupture quad tendons sometimes, somebody out there might have some info on rehabing this sort of thing. It seems if I work it too hard & heavy I will get tendonitis, but lighter weights don’t seem to build much mass. Any pointers on rehab and/or quad exerices would be appreciated. Im a 21 yo fb player. thanks.