The 27-year-old man was walking to work along Herbert Street at about 4pm on Sunday 22 December 2013, when the offender approached him and hit him in the face with a weapon, possibly a metal bar.
He was talking on his phone at the time and was hit several times by the attacker who then ran off. No items were stolen and no demands or threats were made towards him.
The victim was taken to hospital for treatment to injuries to his head and face and received stitches to a cut above his eye.
The offender is described as being of mixed race, about 5ft 11in tall, of medium build and aged 20 or 21. He was wearing a cap, grey bubble jacket and grey trousers.
Police are keen to trace a man who was with two women on the street at the time of the incident as well as any other witnesses.
Detective Constable Jacqueline O’Hara, said: “This appears to be a completely unprovoked and motiveless attack on a young man making his way to work and we are appealing for anyone who can help us identify the offender to come forward.
“We know there was a man with two women who may have witnessed what happened as well as a number of motorists who were in the area at the time and I really need to hear from them.
“If you have any information, regardless how small you think it might be, please get in touch.”
Anyone with information is asked to call police on 0161 856 4502, or Crimestoppers, anonymously, on 0800 555 111.