Definitely go to the Vet and don't wait around to get in either... better safe than be sorry and with a big vet bill >_<
I recently had to take my baby in to the Vet since she was yelping whenever I picked her up a certain way or touched her on the back a certain way.
Originally Posted by Bexasaurus
I would definitely take him to the vet. Rook started having the same problem this last week, I am pretty sure his issue is floating kneecaps though since I can feel them popping in and out of joint. He doesn't cry when I massage or adjust them gently, though. If you pup is that sensitive it may be a whole other issue entirely, and hopefully something the vet can help clear up with a little rest!
You should go to the Vet to see if it is Luxating Patella and what grade he has, just to be safe. It is common in small dogs. Perse has it in both her hind legs with her right being worse than her left. However, I never heard popping or anything until she hit 3 years old, she just walked funny like a rabbit hehe. I've started doing Hydrotherapy to help strengthen and alleviate any pain to make sure it doesn't get any worse.