if you can hardly walk you ought to go to a doctor.
BUT if you've been riding a lot and the cycling is causing the problem,
lay on your back and pull your knee up to your chest. Hold it there for a minute.
Now take that same leg and pull it across to the opposite side of your chest.
Then hold it there for a minute. do the other side as well.

Now if this pain is not FROM cycling, you might try getting on your bike, it might not hurt at all. Or... I have no idea, go see your doctor..

I am not a health care professional, so i can only talk from my own experience.
As the muscles i use for cycling get stronger, I find i have to do this particular stretch more often. (also, the pigeon pose in yoga)

good luck
Mimi