A partygoer suffered a fractured skull and a bleed on the brain after he was attacked outside a Paisley bowling club.
The 24-year-old victim was punched and cracked his head on the ground as he went to break up a fight outside Abercorn Bowling Club .
Violence broke out in the car park of the club during a 50th birthday party around 11.40pm.
Police have now launched a manhunt.
The victim remains in the high dependency unit of the Queen Elizabeth University Hospital in Glasgow where he is being treated for a fractured skull and a bleed on the brain.
Detectives are carrying out a review of CCTV and quizzing potential witnesses over the incident.
Detective Inspector Bob Bowie, from Paisley CID, is leading the investigation and said the other revellers could hold the key to identifying the suspect.
He told the Paisley Daily Express: “The victim sustained a very serious head injury after he was attacked outside Abercorn Bowling Club in Garthland Lane, Paisley, on Saturday night.
“He remains within the high dependency unit at the Queen Elizabeth University Hospital where his condition is described serious.
“He was assaulted by a male as he tried to intervene in an altercation between a group people in the car park outside the club.
“We are currently treating the incident as a serious assault.”
DI Bowie added: “The area was likely to have been busy with people as the function was finishing up, and some of them may have seen what happened.
“I would urge anyone who witnessed the incident to come forward and speak to officers.
“If you have any information at all then we would like to hear from you.”
Anyone with information should phone police on 101, or Crimestoppers anonymously on 0800 555 111.
