A second man was treated at the scene for apparent facial injuries.
Gardaí are appealing for witnesses following a serious assault of two men in Kildare on Sunday (21 August).
Gardaí and Emergency Services were alerted to the scene at Dublin Road in Monasterevin shortly after 12.30pm.
The incident involved a group of people at the entrance of a premises.
A man in his 20s, found unresponsive at the scene, was taken by ambulance to Tallaght Hospital, where his condition is understood to be critical.
A second man, aged in his early 50s, was treated at the scene for apparent facial injuries and removed by ambulance to Portlaoise Hospital. His injuries are not thought to be life threatening.
The scene has since been 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.
