Brown, 46, reportedly has bleeding on the brain and a fractured skull after allegedly being punched by another man.
The former Cat, who played 84 games including the 1994 and 1995 Grand Finals, rushed to the aid of a woman in distress, before the attacker turned on him.
He was allegedly king hit and fell backwards, hitting his head on the concrete pavement.
Brown was taken to Goulburn Valley Hospital, and later rushed to The Alfred hospital after his condition worsened.
He was in a serious but stable condition.
A 19-year-old man from Shepparton was arrested and will face court on January 11.