Google is not your friend! It always scares the crap out of me when I Google for something like this.

I would take him to the GP tomorrow if the limp is still there. How verbal is DS? Can you ask him if it hurts? Is he not doing what he would normally do? If he is in obvious pain, I would take him to the emergency room if I thought it needed seeing to immediately.

Good luck and I hope it is all better tomorrow.