bald spot on belly

my cat has a bald spot on his belly. There are no signs of fleas and he is an indoor cat. I found the bald spot after returning from a ten day vacation. Bubba is a "feral" cat I took in from my parents when they pasted. He has been with me for 3 years and has adapted well. However, he does not do well with strangers and the  pet sitter who looked after him while we were gone said that he would hide in the basement when he arrived to feed and water him. Could this be from nerves?

Hi @hcocopop15 and welcome to TCS and i'm sorry its under these circumstances.  There are various possibilities so its hard to tell from a distance.  Is it just one spot? How big or small? Do you see her grooming it?  Are there any rashes or welts in the bald spot?  Can you take a picture for us?