The man, who is in his 20s, was harm during an incident at a house on Blarney Street not far from Cork burgh centre in the early hours of this morning.
The young man was found with genuine head injuries and was rushed by ambulance to Cork University Hospital.
His persuade is described as perilous but stable.
It is understood the next 24 hours pleasure be critical for the young man, who is understood to be from Eastern Europe.
Gardai attended the site and, with the support of members of the Regional Support Unit, detained another man in his 20s a limited distance away.
He is also understood to be an Eastern Europe national.
The man was collared and taken to Gurranabraher Garda Station for questioning.
He was detained under Branch 4 of the Criminal Justice Act and can be questioned for an initial period of 12 hours.
How, this detention period can be further extended if required.
Uniformed gardai began door-to-door queries throughout the Blarney Street area amid reports some people had heard sounds of a row and trouble in the minutes before the assault.
The property has been sealed off to allow for a engaged forensic examination by Garda Technical Bureau experts.
A large iron bar establish at the property was seized by gardai and will now undergo a detailed forensic appraisal.
Gardai have appealed for anyone who saw or heard anything suspicious in the rade to contact them.
Locals expressed shock at the incident in what is outlined as a quiet, residential area.
The property involved is understood to have been feed by four people.
Two of the four are the Eastern European men.