to make sure he doesn't get an infection you can use blue-kote, i think its actually made for some type of farm animal, don't remember which one, but its totally safe for chins.. just be very careful if you ever use it. it will turn everything purple and will stain.. it will eventually come off the chin, but your clothes will be ruined.
as for a cut, do you have a wire bottom cage floor, could he have cut his foot that way? if so, its good to put something flat, [chin safe] on the floor of the cage so they can rest their feet.
or maybe is there something that might have alittle sharpness to it in there, like maybe he chewed a shelf to a tiny point or something... just trying to think of some reasons why he might of cut it..
definately, talk to a vet, you are right, better to be safe.
jean