The Rail Accident Investigation Branch has confirmed it is investigating the accident which occurred last month.
The RAIB said: “RAIB is investigating an accident to a track worker who was supervising a gang carrying out track maintenance work near Redhill in Surrey.
“The accident occurred at about 10:40 hrs on 24 June 2014. The track worker was struck by a passenger train and suffered serious injuries.
“The injured person was with a gang of eleven people engaged in undertaking repairs to the Up Quarry line between Redhill Tunnel and Quarry Tunnel.
“The train, a passenger service from Gatwick Airport to London Victoria, was travelling at about 80 mph.”