The 29-year-old officer was on the southbound platform at the 23rd Street station on the No. 6 line Saturday evening when he was punched in the head by a man, police said.
The officer fell down and hit his head on the platform; he was later placed in a medically induced coma at Bellevue Hospital Center.
The man was awake by early Monday and was awake and talking with his family. He went home later that day.
The attacker is still at large, police say.
Police released a sketch (above) of the attacker, who they said was with his daughter on the platform. The NYPD is asking anyone with information to call 1-800-577-TIPS.