What could be wrong with our cat?

My wife just called this to my attention. One of our cats has what seems to be a hole in his throat area. Fur is gone around a circular spot, and there seems to be some blood in the area. He hasn’t acted like he feels bad, still has his usual loud meow, eats well and chases squirrels around the yard. But that just isn’t normal. We have a vet appointment for Thurs. this week, earliest we can get him in. Any ideas what this could be?