Double Olympic road cycling champion Remco Evenepoel was rushed to hospital after hitting the open door of a post office van in Brussels during a training run Tuesday.
The Belgian won the individual time trial and the road race at the Paris Olympics and won the best young rider's jersey at the Tour de France in July.
Evenepoel's father, Patrick, told Belgian media he was as yet unaware of his son's condition as he rushed to be with his son at a hospital in the capital.
"Remco was transferred to the Erasme hospital in Anderlecht (in Brussels). We're still waiting to see how he's doing. We're on our way to the hospital," he told daily newspaper Het Laatste Nieuws.
Evenepoel successfully defended his world time-trial title in Zurich in September and is a former winner of the Vuelta a Espana.