The wall collapsed Friday on the northbound platform at the Cortlandt Street R-train stop, the New York Post reported.
Service was slowed along the line for about four hours, officials said.
MTA officials said the cause of the collapse had yet to be determined, but a maintenance worker at the scene said recent wet weather was likely a factor.
"It's water damage," he said. "It's just old, and it's raining."
Workers covered the damage with plywood and an MTA official said the station was "deemed safe."