A man is in a critical condition after being punched during fighting outside the Printworks near Dantzic Street and Thornily Brow in the early hours of Saturday morning
From enquiries so far, it is believed a large fight of around 15 people took place.
A man in his 50s tried to intervene and was punched in the face and knocked unconscious.
He was taken to hospital with a serious head injury where he remains in a critical condition.
A second man, who is in his 20s, was also taken to hospital for bruising and cuts.
A 25-year-old man was arrested near to the scene on suspicion of affray and a 32-year-old woman has since been arrested on suspicion of assisting an offender. They both have been released under investigation.
Extensive CCTV continues and detectives are appealing for anyone who might have witnessed the fight but hasn’t yet spoken to police.
Detective Inspector Mark Davis from GMP’s City of Manchester team, said: “This was a large brawl in the city centre at a time when a lot of people would be leaving bars and clubs.
“It might be that you witnessed something but didn’t think to contact police at the time. If so, please get in touch with us as soon as possible.
“Just one punch on a night out has the potential to change people’s lives and a man has been severely injured as a result.
“We also know there were lots of cars in the area and I would urge drivers to check their dash cam footage to see if there’s anything on there that could help us with this investigation.
“We also believe there might be further victims who were injured and again, I would ask you to call us too.”