The peloton crashed at a reported 60km/h with 22km to go in the 197.1km stage from Dunkerque to Iwuy in northern France. Around 50 riders went down, with only a small front group avoiding the crash. Jens Debusschere (Lotto Soudal) went on to win the stage.
The crash blocked the road. Frederik Frison (Lotto Soudal) fractured his pelvis and three riders from Veranda's Willems-Crelan needed to go to hospital, but Vandenbergh was the most seriously hurt. He was reportedly unconscious and bleeding from his nose and mouth. That scared his teammates, who screamed for urgent medical assistance. He was quickly given oxygen and taken to hospital.
Initial reports in Belgium suggested Vandenbergh had suffered a brain haemorrhage but the AG2R-La Mondiale team denied this, confirming on Wednesday morning MRI scans had diagnosed concussion.
"He doesn't have a brain haemorrhage. He has a concussion and bruising. He had a good night. He'll have another scan today and then we will know if he is allowed to leave the hospital," press officer Yves Perret told Belgian media.
Wanty-Groupe Gobert directeur sportif Hilaire Van der Schueren was angry that the UCI jury had not neutralized the race after such a major crash. His team is still struggling to handle the shock of crashes after the death of Antoine Demoitié at last year's Gent-Wevelgem and the serious injuries to Lotto Soudal's Stig Broeckx.
"I called the Spanish jury chief. Many riders are traumatized by all the falls they experienced last year," he told Het Nieuwsblad.
"The peloton was riding at 60km/h on that stretch of road. This crash recalled Stig Broeckx's fall. The UCI is always talking about respect and safety, but if something happens, they just continue the race."
The 4 Jours de Dunkerque continues today with a 171km stage around Saint Quentin.