Police said officers responded to the South Austin neighborhood's 300-block of North Central Avenue around 2:30 a.m.
A 37-year-old man told officers he was on a Green Line train when someone approached him, took out a sharp object, and demanded his property.
The victim struggled with the suspect, a male of an unknown age, and suffered a cut to his arm, police said.
The victim was taken to West Suburban Hospital, where he is listed in good condition.
There is no one in custody, and Area Four detectives are investigating.
The stabbing comes as the CTA is launching a new security program in partnership with police.
It is called the Transit Rider Interaction Program, or TRIP.
Police officers will line platforms and check in with train operators. Officers will then ride to other stations to do the same checks. The CTA hopes these new patrols will deter crime.
Police did not immediately provide further information about Friday morning's stabbing.
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