The diner, who has declined to be named, was horrified after biting into the burger at the firm's town centre branch in High Street and discovering a piece of chicken with what he says were specks of green mould.
"I would have eaten it if I hadn't spotted it in time," he said. "It was disgusting."
After complaining to staff, the customer was given a new burger.
"They just took the burger with the mould in and replaced it with a new one. They didn’t really look into it or say anything to us.
We have contacted KFC for comment.