Injured Cat found

I just found a smaller (possibly only a year or two old) male cat. He has some very nasty teeth marks on his head - I’m assuming he was attacked by a coyote. His left eye is swollen shut, but there is an eye in there. He is very affectionate, so l believe that he belongs to someone. I have him I. My garage, it’s heated. I have an elderly cat who really doesn’t like his space being invaded. What can I do for this little guy. I gave him water & wet food. I don’t know what to do. It’s heartbreaking to look at him. I definitely need some advice. Where can I do for him?