Why does my Dog's behavior change?

There is a lot of information you can read online about "counter conditioning & positive association" to build your dog's confidence level. That injury sounds pretty serious (more than just a little scuffle) so it's understandable that he's leery of others now. If the injury happened over playing with toys and/or fights and resource guarding food/treats, that would explain why he's not as excited about those things (negative association was formed). It will take time and patience.

Poor little guy! For Cinnamon to be hospitalized for weeks, WOW, he must of been in critical condition. That is scary! It is truly amazing how resilient our pets are. I am happy to hear that physically he is back to normal and doing well. However, it does sound as if he is still traumatized from this situation. You mentioned that he doesn't like to go outside or play with his toys anymore, just out of curiosity, I am wondering if the fight that happened outside and if it was over a toy or something that the other dog was able to guard? (not that it makes a difference, just curious) I would recommend is that you take Cinnamon to a Board Certified Dog Behavior Specialist. The reason why I am so specific is because anyone can call themselves a "Behaviorist" but a "Board Certified" means that he/she not only graduated from Veterinary School but also than specialized in animal behavior. physically Cinnamon is better but not emotionally. Just like Humans, pets can get PTSD. And although I don't know all details (but working in the Veterinary Field for over 18 years ) I do know with a hospitalization stay for weeks, that was not just a "bite" but a full on Vicious Attack. I send you my prayers and wish you both the best of luck!

Sorry to hear. I have had few situations where my doggy was attacked by a dog. Usually off leash with a very irresponsible owner who did not care at all. Ugly situations. I have had many trainers and finally hired a Board Certified Dog Behavior Specialist who charges over $140 an hour. I had her come to me few times and she told me that my dog has a PTSD and will never be the same. I just have to work with him, but it will never be the way it was before. When dogs are traumatized, it's usually forever.