A second man was treated at the scene for apparent facial injuries.
Gardaí in Kildare are appealing for witnesses after two men were seriously assaulted in Monasterevin early this morning.
Shortly after half-past midnight, a man in his 20s was found unresponsive on Dublin Road.
He was taken by ambulance to Tallaght Hospital, where his condition is understood to be critical.
The incident involved a group of people at the entrance of a premises.
A second man, aged in his early 50s, was treated for facial injuries at the scene before being brought to Portlaoise Hospital.
His injuries are not thought to be life-threatening.
The scene is preserved for forensic examination and no arrests have been made at this time.
An incident room has been established at Kildare Garda Station.
Gardaí are appealing for any witnesses to this incident to come forward and for those with camera footage to make it available to them.
Anyone with information is asked to contact Kildare Garda Station on 045 527730 or the Garda Confidential Line 1800 666 111..
