The victim was walking on Fishamble Street outside Christchurch at around 2am when he was savagely assaulted and robbed.
Sources say it appears the man may have been punched to the ground and kicked, and possibly assaulted with a weapon.
A taxi driver who saw the victim staggering along the street with obvious injuries came to his aid and raised the alarm.
The victim was taken to St James's Hospital where his injures are described as serious but not life threatening.
The scene of the attack was sealed off by gardai pending a forensic examination by members of the garda technical bureau.
Garda tape stretched from the railings of Christchurch to the perimeter wall of the Dublin City Council offices, and a cobbled laneway between the two buildings was also sealed off.
No arrests were made in the immediate aftermath of the attack, and gardai at Kevin Street are examining CCTV footage from the area in a bid to progress the investigation.
They are seeking help from any witnesses and have urged them to come forward and contact them on 01 6669400 or on the Garda Confidential Line 1800 666 111.