A 48-year-old man was on a train about 8:10 p.m. in the 100-block of North State Street, near the State and Lake stop, when a male suspect approached him and started a "verbal altercation," police said.
The suspect then cut the man's arm with a knife and ran.
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The man who was injured was transported to Northwestern Memorial Hospital in good condition, police said.
Area Three Detectives are investigating.
A man was stabbed on a Red Line train near the Cermak-Chinatown station earlier this month, police said at the time.