Keeley's bum leg

I don't know what I'm going to do with this pup! It seems that Keeley really over did it at his party yesterday because he's favoring his bum leg today.
It feels like there's always something wrong with his left hind leg. When he was just a little pup he had a greenstick fracture from a bad landing and then last year he somehow managed to break a toe on that same leg.
Near the end of his party, I caught him hopping around on only 3 legs and I immediately said it was time for him to take it easy and no more wrestling. Apparently, I was the only one who noticed him favoring that leg because everyone else seemed to think that I was overreacting.
This morning he seemed fine and so we went to the dog park. But as soon as we got to Minooka, he started doing his 3 leg hop. If you look close a the picture below, you can see that he's not using his left hind leg.
Keeley doesn't complain or whine but I figure it must be hurting if he's choosing not to use that leg. So we took him home and gave him a dose of Metacam. He took a nap and seems fine. Just to be safe, I think he's going to stay home from daycare this week and rest.