The man was set upon after the team's 2-0 win over Bolton Wanderers.
It happened, witnesses say, near a bus stop on Eyre Street.
Eye witness accounts on a fan forum page described the man lying in a "pool of blood" after the incident.
One man who posted said he was nearby when it happened.
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"[I] Didn't see what happened to the lad on the floor but he certainly had blood at the side of his head," the man said.
"[He] only looked in his 20s to me but I didn't stand and gawp."
Others described tense scenes after the match.
"It was getting very edgy towards St Mary's Gate after the game," one forum member said.