Minor quad/knee injury

I wondered if I'm doing everything right or if this problem is familiar to anyone. I unexpectedly developed a minor injury that caused friction above my upper left knee, in the quad area. Hard to say whether you might call it a ligament strain, a knee injury or a quad injury. Basically the discomfort is felt down the very lower inside thigh just above the knee. I first detected it as a burning sensation running down the leg from that area.
I had 3 days rest which I know is very little. I did some squats and stretching. I risked riding today and am relieved that I didn't have any major problems. Having said that I'm sure the area has lost strength and I daren't ride as hard as I would normally. I'm making an effort to stand more often when hill-climbing to take stress off the knee.
Anyone have any idea if this is a common problem and is there any way I can strengthen the inner part of the thigh. I wouldn't ride my bike at all but there was definitely no discomfort today, just a very slight sensation the injury could still flare up again.