An Irishman is in a critical condition after he was found unconscious outside a Canberra nightclub in the early hours of Sunday morning.
The unnamed 41-year-old man is understood to have received a single blow to the head.
He was rushed to Canberra Hospital after being treated at the scene by police officers and security guards.
The Depatment of Foreign Affairs is providing consular assistance to the man's family.
Police said the incident was caught on CCTV security cameras and that they are seeking a suspect.
"The victim sustained what appears to be externally very little.
''However, on examination at the hospital, he's got severe cerebral hemorrhages and he's had to undergo surgery," Detective Sergeant Matt Innes told reporters today.
"We expect to make some arrests in the next couple of days," he added.