Investigators have been told the pair were involved in a verbal dispute before one smashed a glass over the other’s head shortly before 10 p.m.
The offender left the scene on foot and has yet to be found.
A 36-year-old Queensland man received medical treatment for his injury.
The incident occurred during the Dreamtime ‘G match between Essendon and Richmond.
While police said they were satisfied with the behavior of most fans at MCG last night, 10 people were evicted from the stadium, including a man who ran onto the field in the late stages of the game.