What Causes Pain Below Knee Cap During Workout?

I was playing basketball a couple weeks ago a took a bad fall and landed funny on my left leg. It hurt a lot near the top, just below the knee cap, on either side of my leg. It felt deeper than the usual post workout muscle ache, almost like down to the bones. It feels OK now, except when I do any hard workouts it starts to ache. And it hurts a lot when crouch low on it. What could the problem be?