Olympic BMX silver medallist Jelle van Gorkom is in a coma after a training accident on Tuesday.
The Royal Dutch Cycling Union said the 27-year-old had "broken ribs, a fracture in the face, a tear in the skull and damage to the liver, spleen and kidneys".
The incident occurred at the National Sports Centre Papendal in Arnhem.
Van Gorkom won silver medals at the 2015 World Championships and the 2016 Rio Games.
Bas de Bever, the Dutch national BMX coach, asked that the rider, his girlfriend and his family be given "peace and privacy", while Jochem Schellens, director at the National Sports Centre Papendal, added: "It is a terrible accident and... we wish them all the strength in the coming period."