My cat was attacked by a weird ill cat

Hello,

Just in front of my house, I happened to hear sounds of cats fighting. Since they were massive, I tried to separate my cat from another cat. The cat he was fighting was probably starving, very little, moreover his mouth was drooling, and he had scabs and crusts all over the face. 

I wonder if this cat was ill, what kind of illness it could be and how it could affect my cat. Any diseases my cat could get from it ? Anyway to protect him from these ? 

Thanking you in advance

Is your cat vaccinated for rabies? Fiv/felv?

Facial lesions can be caused by anything from feline herpes virus to allergies, or ear mites, or even mange mites. See if the humane society can borrow you a trap to catch the poor sick fellow.

If it is mites, an application of Revolution will help tremendously for the stray.  Sometimes there are trap neuter return programs that will allow you to spay neuter feral cats. They can be free or low  cost.

It was most likely an intact tom cat. Tom's are noticeably more aggressive as they have so much testosterone.

Cat not vaccinated for rabies, but we can't do it here since my country is rabies free. Vaccination against rabies is only possible here if the cat travel. 

He was only primary vaccinated for the other things, some need more than 1 injection.