Well for starters ring worm is just a fungus that you can catch easily from anywhere and sometimes it can be hard to get rid of so if you think your dog has it don't touch it cause humans can catch it to I know cause I've had it. But it starts out kinda small and it is circular and kinda pinkish red it depends but the circle will grow also the dog will go bald in that spot so you can see it very well and if the spot grows larger it is definitely ring worm. My grandmother bought some cream stuff with iodine in it from a pharmacy and it looks kinda brown and the smell is strong I forgot what it is called but that stuff works really well for getting rid of the ring worm
It could be - they do get round bald spots. You could have a look here and see if the pictures look much like your dog's condition.