A man asked the pensioner if he wanted to buy two mobile phones before threatening and assaulting him during the incident on Northgate.
The victim then handed over his wallet from which the other man took Â£40 before making off towards Daisy Hill.
The incident happened at around 9am on Saturday June 10, but police only released details today. (Mon June 19)
The suspect is described as a thin 5ft 8in tall unshaven Asian man with short, dark grey hair.Any witnesses to the incident are asked to contact police on 101, quoting crime reference 13170266250.