The assault took place in the early hours of Sunday (17 April).
A statement has been released by Gardaí following an incident in Dublin City City Centre in the early hours of Sunday, 17 April, 2022.
Shortly after 2.30am, Gardaí and emergency services arrived on D'Olier Street, near the junction with Fleet Street, after a man in his mid 20s was seriously injured in the course of an incident.
The injured man was treated at the scene for an apparent head injury and removed by ambulance to St James's Hospital. His condition is understood to be critical.
In a follow-up operation, a search of a house was conducted under warrant in Kildare by investigating Gardaí and a man in his 30s was arrested in connection with the incident. He is currently detained under Section 4 of the Criminal Justice Act, 1984 at Pearse Street Garda Station.
A forensic examination at the scene of the incident has been completed.
Investigating Gardaí are appealing for witnesses to come forward and are also appealing to those with camera footage from the location at the time of the incident to make it available to them.
Anyone with information is asked to contact Pearse Street Garda Station 01 6669000, the Garda Confidential Line on 1800 666 111 or any Garda station.
Investigations are ongoing.