James Tynan, aged 25, from Johnstown in Co Kilkenny, was fighting for his life after the assault in Thurles at about 1.30am on Sunday.
It is believed that outside a nightclub a person unknown to Mr Tynan punched him once in the face. He fell to the ground, severely injuring his head.
The incident happened close to where another Johnstown native, Kilkenny hurler PJ Delaney, was assaulted in Sept 1999.
Mr Tynan had been socialising in Hayes’s Hotel before being attacked in Liberty Square.
Gardaí were called to the scene and arrested a 22-year-old man, understood to be from Co Tipperary, who was last night being questioned by gardaí under section 4 of the Criminal Justice Act.
Mr Tynan was rushed to South Tipperary General Hospital in Clonmel in the early hours of Sunday and has been in intensive care since. His worried family have been keeping a vigil by his bed.
He is the youngest of six children and works with his father, Pascal, in the family meat wholesale business. His girlfriend, Fiona Morrissey, is also from the area and her parents run a shop in the town.
Mr Tynan was described yesterday by a Johnstown local as very unassuming and well-liked, while his family are well-known through their business and community connections.
There was no one at their house on Main St, Johnstown, yesterday as family members remained with Mr Tynan in his hospital room in Clonmel.
The incident has left the community “stunned”, said one local person, and has revived memories of the assault on former Kilkenny All-Star hurler PJ Delaney, who was attacked in Thurles in 1999 and left in a coma for nine days and unable to return to full-time work for nine months.
“It’s hard to believe it’s happened to another Johnstown person,” said a neighbour.
Investigators have been studying CCTV footage from various businesses in the area, as well as speaking to witnesses who were in the popular nightspot at the time. They have appealed for anyone with any information to contact them on 0504 25100.