The fight happened just after midnight at Butch McGuire's on State and Division, according to Chicago police.
Two men, 24 and 27, got into an argument at the bar. Police said the 24-year-old broke a glass cup on the 27-year-old.
The 27-year-old victim was taken to the hospital in critical condition after the glass shards cut his neck.
The 24-year-old was taken into custody and charges are pending.
No other information was available.
Chicago police are investigating.
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