The brutal attack is believed to have happened in the early hours of yesterday morning, Friday, September 25.
Detective Inspector McKee said: “It is though that a sum of cash was stolen from a man by two other men.
“Immediately after the robbery, he was sexually assaulted.
“The incident is thought to have happened in the area of Dudley Street sometime in the early hours of Friday morning.”
DI McKee added: “The man is clearly distressed and we would ask for public support in our efforts to identify the two involved.
“I would ask for anyone who was in the area at the time to contact detectives on the non-emergency number 101.”
Alternatively information can be passed anonymously through Crimestoppers on 0800 555 111.