The incident took place shortly before 2am at a terraced house on St Vincent’s View, close to UCC.
Gardaí say the man — an Irish national — was assaulted and taken to Cork University Hospital with “serious” head injuries following an incident at the property.
Gardaí were preserving the scene this morning ahead of a technical examination.
It is not yet known if the man’s injuries are life-threatening.
A Garda spokesperson said: “The male suffered a serious assault and was taken to Cork University Hospital with head injuries. Gardaí were called to the scene at approximately 2am and are preserving it pending a technical crime scene investigation this morning.”
Gardaí at the Bridewell Station on the Coal Quay are appealing for witnesses to the incident.
The assault is the latest in a growing number of incidents in the city and county, with the highest number of assaults logged since records began in 2003.
The Central Statistics Office recorded 1,132 assaults in the city last year.
In the first three months of 2018, 220 assaults were logged by gardaí in the city and almost 400 in the entire county.