Hello & welcome, I am Dr. B, a licensed veterinarian and I would like to help you with your wee one today.
Based on your signs, I would be suspicious that he may be showing these signs due to discomfort (where the oral signs could be a reaction to wanting to lick an irritated site he just cannot reach). Otherwise, we can see similar signs if there has been damage to the tongue/mouth, if the cat is a carrier of herpes virus (where the stress of the fight he was in has lead to a viral flare-up), or if there is potentially an infection brewing in the wound tissues. And all of these can potentially make him feel unwell and put him off his food.
In this situation, you have taken the right course of action so far. And as long as he is breathing comfortably,has pink gums, and the wound is not bleeding; we'd be fine to wait until Monday to have him seen. In the meantime, we do want to make sure he drinks and potentially tempt him with favourite foods or light diet options (ie boiled chicken, white fish, scrambled egg). Once his vet is open, then can check this wound (as a puncture stitching is likely unnecessary) and start him on antibiotics and kitty safe pain relief (ie Metacam) to facilitate his healing and settling this all for him.
Finally, just to note in case you were keen to have him seen today, some veterinary practices in our country have Sunday office hours. As well, I wanted to mention that most veterinary practices here do have contingency plans for emergency care for their patients even when they are not open. Therefore, it is worth ringing the practice. If they are open, you can get him seen today. If they aren't, then they will likely have a message to direct you on how to contact their out of hours service. And if you don't have a vet you can find one local to you, you can check the RCVS Register (HERE) to find your local Vets Now (LINK) who are open all nights/weekends. In any case, if you wanted to get him checked out sooner then there are options to have him seen today too.
I hope this information is helpful.
If you need any additional information, do not hesitate to ask!
All the best,