Investigators have been told the pair were involved in a verbal dispute before one smashed a glass on top of the head of the other shortly before 10pm.
The offender left the scene on foot and is yet to be found.
A 36-year-old man from Queensland was provided medical treatment for his injury.
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The incident happened during the Dreamtime at the ‘G match between Essendon and Richmond.
While police said they were pleased with the behaviour of most fans at the MCG last night, 10 people were evicted from the stadium, including a man who ran onto the field in the dying stages of the game.
