The man, who was in his twenties, was taken to Cork University Hospital, where he is currently in a critical condition.
Another guy, it is believed, has died as a result of a cardiac attack.
Access to the scene in the Hollyhill neighbourhood has been denied to the general public.
The investigation into the event is still ongoing, according to the Gardai.
An official statement said: “Garda are investigating an assault that occurred in the Hollyhill area of Co Cork in the early hours of this morning, Friday 28th January 2022, and is under investigation.”
An unidentified guy in his twenties has been transported to Cork University Hospital for treatment of serious injuries.