I have a stray cat coming around for a long time now, and I always feed him I am a bit worried about him as?

Nothing you can get to put in his food. Call your local animal control, and ask if they have humane traps to borrow, or if they can refer you to a trap/neuter/return group. Don't feed him for a day, and bait the trap with food as they will instruct you. Get a standing appointment with the vet so that you can drop him off after you've trapped him. Warn the vet about his behavior, and they will likely give him a whiff of gas to examine him. They can treat what is wrong with him and get him up to date on vaccines as well. And if he's not neutered, then perhaps you will have the vet do that also. He will be much better off getting vetted, and be sure to keep his rabies certificate. Good luck - but trapping him is the best option. The vet can give him a long lasting antibiotic shot if needed.

You can try a can of soft cat food and mix in a little bit of tetracycline. You can get tetracycline at the feed and ranch store. It's for chickens. Mix a quarter of a teaspoon in with the food use a measuring spoon. If he has a bacterial infection it might help out.

i would say take to the vet

He needs professional help as if it's cat flu it can become pneumonia and kill him. See if you can trap him in some way, maybe by leaving a cat carrier open with some treats at the back and then shutting the door on him. Or, call a vet for advice on what to do.

Why don’t you put the food inside the house and see if he’ll come inside then you can try to catch him.

You can also try to pet him and see if he lets you. If he does then try picking him up.

You can try putting a portable cathouse to give him shelter from the weather.