The stabbing occurred in the 4600 block of West 59th Street.
At about 7:30 a.m., a 41-year-old man, a 48-year-old man and a 29-year-old man were on a train platform when an unknown male offender began a verbal altercation with them, police said.
The offender produced a knife and began swinging it at all three victims.
The 29-year-old suffered a laceration to the left arm, and was transported to the hospital in good condition.
No other injuries were reported.
Two other attacks happened on CTA trains or CTA platforms Saturday night.
A 50-year-old man was stabbed in the head and pushed onto train tracks on Chicago's West Side at about 9:37 p.m.
A 39-year-old man was on a Blue Line train when he was stabbed in the face Saturday night at about 10:45 p.m.
No one is in custody in any of these stabbings.