It happened on Bottrill Street close to the church between 7.30am and 8am on Friday (13 December).
A man in his 40s was walking along when he was approached by an unknown man.
The man is reported to have punched the victim to the side of the head before attempting to grab his rucksack.
The man did not manage to take the rucksack and left the area.
He is described as being white, around 6ft tall and is believed to have been wearing a dark jacket, dark trousers, black gloves and a hat.
Enquiries are currently ongoing but officers would like anyone who witnessed the incident, or who saw anyone acting suspiciously to come forward.
Anyone with information is asked to call 101 or Crimestoppers anonymously on 0800 555 111 quoting incident number 58 of 13 December.