Double Olympic road cycling champion Remco Evenepoel says he faces "a long journey" after breaking a hand, ribs and shoulder blade in a collision with the door of a postal van during a training ride.

The 24-year-old Belgian, who won road race and time-trial gold at the Paris Olympics, was rushed to hospital Tuesday after striking the open door of a stationary van in Brussels while preparing for the new season.

"After a scary accident on training yesterday, I underwent surgery last night and everything went well," Evenepoel wrote on social media Wednesday.