A man was knocked unconscious during a fight in Drouin in the early hours of Sunday morning.
Police reported a 48-year-old man from Cape Woolamai was taken to The Alfred Hospital in Melbourne with head trauma following the altercation.
They allege an argument broke out between several patrons at about 12.30am inside the Drouin Family Hotel.
After leaving the premises, five men challenged the 48-year-old to a fight, police said.
Baw Baw CIU are investigating and have interviewed four men, a 34-year-old from Drouin, a 41-year-old from Labertouche, a 48-year-old from Narre Warren and a 46-year-old from Wimbledon Heights, in relation to the incident.
A fifth man has not been identified.
Police said enquiries are ongoing and appealed for anyone with information which may assist investigations to contact Baw Baw CIU.