The incident, which happened at 11.45am on Wednesday morning, occurred at Kentish Town station, Transport Police have confirmed.
British Transport Police added that the unidentified man ‘may have been pushed’ from the platform at the zone 2 station, and that they are treating the incident as suspicious.
The man sustained severe injuries and is currently being treated at a hospital in Central London.
One witness to the incident said they felt ‘physically sick’ by what they had seen, while another said that the driver had sounded ‘panicked’ over the tannoy system.
Meanwhile London Ambulance Service confirmed they had treated a man at the scene, taking him to hospital for further treatment.
The police have released a CCTV image of the man they are searching for in connection with the incident.