Pain in Knee when Straightening Leg and Putting Weight on it

Patient: When I straighten my leg and put full weight on it, the base of knee just below the patella feels sore. It almost feels like my knee slightly goes back too far and feels unstable. I’m not sure if it’s from an old injury when I was running and my leg straightened out and I ended up landing all my weight into my knee, but the soreness has become worse as I’ve been doing zumba. Do you happen to know what could be wrong?