Police were called to Exchange Square on Sunday (18 July) at around 5.45pm to reports of an assault near the shopping centre.
It is understood the security guard, aged 43, was on duty at the shopping centre when he was assaulted by members of the group.
He was also subjected to racial abuse, the shopping centre said.
The member of staff was taken to hospital with minor injures, police said.
Members of the group can be heard shouting and screaming, with some people seen pushing their way through the crowd.
Police were forced to issue a dispersal order in the area until 12.01am this morning (19 July) as a result of the incident.
No arrests have been made and an investigation has been launched.
A spokesperson for GMP said: “Officers were called around 5.45pm on Sunday 18 July to Exchange Square, Manchester to a report of an assault.
“Officers attended and enquiries established a large group of people – believed to have been youths – had congregated in the area and a 43-year-old man had been assaulted by members of the group.
“The man was taken to hospital with minor injuries.
“A dispersal order was subsequently issued for the area until 00:01 today (19 July).
David Allinson, Centre Director, Manchester Arndale, said: “We are aware of the violent and entirely unacceptable incident which took place outside the centre yesterday afternoon (Sunday 18 July), involving a group of individuals and which resulted in the physical assault of a member of Manchester Arndale’s security team and racial abuse towards the same member of staff.
“We reported the incident to Greater Manchester Police, and we will continue to support them with their investigation.
“The safety of shoppers and staff is of paramount importance, and we cannot tolerate such behaviour and treatment of our hard-working colleagues under any circumstances.
Source – manchester evening news