At about 1.30am on Sunday 16 January 2011, the 24-year-old woman, who had been on a night out, was walking to a car on Wright Street when a group of about seven men approached them.
They verbally abused her before one of the men hit the victim to the face, knocking her to the floor.
The offender, who was in the company of six others, is described as being an Asian man, about 25-years-old, of slim build, about 5ft 5in tall with spikey black hair.
He had a local accent and was wearing a white shirt.
The offenders ran off towards Yorkshire Street. Detective Constable Simon Halliwell said: "This was a completely unprovoked and incomprehensible attack. "We have carried out a number of inquiries to trace the offender but we do need witnesses, or anyone with information, to get in touch."
Anyone with information is asked to call police on 0161 856 8965 or call the independent charity Crimestoppers anonymously on 0800 555 111.
These unprovoked pack attacks on lone infidels have reached epidemic proportions and are known as 'Street Jihad'