I hope it's not, but it sounds like an ACL tear. My bully tore hers a few months ago. She is also really hyper, and the vet said that it's a very common injury for hyper dogs. She had her limp for about 3 days before I took her in, thinking it was sprain or something less severe. She also wouldn't put pressure on her foot and would favor it when she was sitting. She didn't whine until I picked her up and must have hit it just wrong, she is a tough girl. Good luck!