Police said it happened at the 95th/Dan Ryan Station in Roseland just after 5 p.m.
Two women, 31 and 23 years old, were involved in a physical altercation with a group of unknown people, police said.
Police said the two women were on the platform when the group battered them. During the fight, the 23-year-old was slashed in her shoulder.
The victim was transported to Christ Hospital in good condition, police said. The 31-year-old refused medical attention.
The offenders fled on foot in an unknown direction.
There is no one in custody and Area Two detectives are investigating.
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