Yes call Animal Control...my dog got attacked by another off leash dog and because I felt bad for the owner, I thought, we can work something out and she can pay the vet bills. But the more I thought about it, this could happen again and it could be a child the next time. The dog came from across a large field just to attack my little dog. You could go to the owner and say here are the bills I've paid so far to treat my dog - the only thing you can do in terms of getting your money back is to either ask him and hope he's a normal person with a conscience who will reimburse you for your vet bills. Or sue him in small claims court. At least that was what I was told where I live in Canada. I did end up reporting them to Animal Control - I don't think they had a limit as to the time period of when I had to report it but they did say that the sooner the better as punishment usually is more effective that way. Anyway, they got charged $120 for the dog being off leash and $270 for the attack. The AC guy went to their house and gave them a speech on leashing their dogs and gave them their tickets. In this situation, I would hope that it would have hit them hard as they claimed to have no money. I'm not trying to sound vindictive but, apparently, this dog attacked another small dog previously and it wasn't reported. So the owners didn't learn.
I hope your guy recuperates and that you can get this guy to pay for his crime. Even if the dog was a chihuahua, the owner has the responsibility to control his dog whether it be with strict training or a leash. Good luck and let us know what happens....
