Quite often with men's shirts, the collar will wear through before the body of the shirt. I turn the collars on MrL's shirts, and usually get at least another year or so out of them, office, work and casual shirts.
Carefully undo the seaming where the collar is sewn into the neck.
Turn it over, ready to be reinserted into the opening made when you removed it
Pop it back in, and pin in place, through all thicknesses
Tack securely in place ready for sewing, remove the pins
Sew securely, remove tacking, and press well.
"New" collar, ready to go