I was using the leg press on my 3rd set incereasing weight every set and I felt a bad pain in my left knee. So I immediately stopped and waited about 5 minutes and it was still there so I did not continue. Is it a sign of a serious injury. What can it be? It cant be tendonitis because I only train legs once a week and it is the first time I felt it. There is alot of pain when I bend my knee to sit down or try any leg excercises. Will it go away? What can it be?