My pup ran into a post (yeah he was reallllly ball focused), bounced off and kept going. he came up limping. I would limit activity. He may have pulled/strained a muscle and it's a bit sore. No jumping, running like a crazy person, etc. You may have to leash him and do more crate rest. My pup was on crate rest for 2 weeks and then I kept him on reduced activity for another 2 just to make sure. However, his was a bit more ... extreme. Maybe just make him take it easy a few days and see how he does.
Xan Varik von Fernheim (born 4/3/13)