I found a wound on his side, a puncture that looked like it was getting infected and that I am now treating. If it gets bad, I guess I'll have to get more antibiotics for him, but he cannot live on meds like that. He's not been outside since that last fight and has been using the litter box against his will, LOL.
If it looks like it's getting infected I would probably put him on antibiotics anyway just in case just to be safe but that's just me. If he's been inside, hopefully he won't need any antibiotics after that if you catch the other cat. That's great he's been staying inside though!