The 23-year-old was taken to hospital after the incident in the car park to the rear of Walker Road just after 8pm on December 27.
Police said the man was taken to hospital but has since been discharged – with the scene sealed off as forensics sweep the area.
A spokesman for the force said: "We sealed off the scene for a forensic search and are working to understand more about what has happened. Officers are carrying out extra patrols in the area to support the community.
"We understand incidents of this nature are shocking and we will thoroughly investigate all lines of inquiry.
"Anyone who heard or saw anything suspicious in the area – or has dash-cam or CCTV footage – is asked to call us on 101 or message us on Live Chat through our website and quote log 3466 of 27 December."
Information can be passed anonymously via the independent charity Crimestoppers on 0800 555 111.