The 41-year-old victim and a 39-year-old woman went to a unit block on Todd Street, Warrawong, a suburb of Wollongong, on Saturday morning, where a 34-year-old man lives.

Police said the younger man started arguing with the 41-year-old, picking up a vase, smashing it and swiping him on the chin, causing a deep gash.

The 34-year-old also punched him in the face several times, while the woman tried to stop the fight.

The injured man tried to escape the unit block by climbing out the window, but slipped while trying to walk along the window ledge and fell to the ground. He was flown to St George Hospital with serious head injuries, including a fractured skull.

‘‘(The fight) was in relation to one male saying bad comments about the other male’s brother,’’ Lake Illawarra local area command duty officer, Inspector Bryan Rugg, said.

‘‘It’s a bit like ‘you’re slagging off my family’.’’

He said it was unclear how the two men knew each other.

Police may charge the 34-year-old man, but investigators are appealing for any witnesses to come forward.

‘‘The 41-year-old has no recollection of the incident, probably because he has a head injury.’’

Anyone with information was asked to call Crime Stoppers on 1800 333 000.