The southbound Red Line was briefly rerouted to the elevated tracks around 7 a.m. while power was cut during the emergency response.
The man fell from the platform onto the southbound subway tracks at 230 S. State St.
The man was not hit by a train and did not make contact with the third rail, said fire media affairs spokesman Quention Curtis.
Howard-bound trains were unaffected, the CTA said.
The STNG Wire contributed to this report.