The boy told police he was attacked in a tunnel underneath Clayton Road near City Hall Friday afternoon.
Officers have questioned several people, but have not found a suspect.
The boy says the man was wearing hospital clothing including a teal beanie hat, teal shirt and pants, medical gloves and a surgical mask.
The suspect is described as a black man with a goatee, in his forties, and about 6 feet tall.
Anyone with information is asked to call Clayton Police.