Michael Goolaerts (Vérandas Willems-Crelan) was airlifted to the hospital after being knocked unconscious in a heavy crash at Paris-Roubaix on Sunday, emergency services said.
A statement from the team read: "It is with unimaginable sadness that we have to communicate the passing of our rider and friend Michael Goolaearts".
It added that he "died of cardiac arrest, all medical assistance was to no avail".
Sagan eventually won the race after accelerating 55km from the finish line at the Roubaix Velodrome to catch the day's breakaway riders and get rid of the strongest of them, Swiss Silvan Dillier, in a sprint finish.
TV footage of the 257km race showed Goolaerts lying unresponsive on the side of the road as the peloton passed him.
The race, part of the International Cycling Union World Tour, was won by Slovakia's Peter Sagan with the result now immaterial.
Sagan thus became the first rider since Bernard Hinault in 1981 to win the Queen of the Classics in the rainbow jersey of a world champion. "I'm exhausted after this race but not as exhausted as in previous years when I didn't win it for some reasons", Sagan said.
Veranda's Willems-Crelan said that the 23-year-old had suffered a cardiac arrest, receiving emergency treatment from medical staff at the scene.
In the Trouee d'Arenberg, one of the toughest cobbled sectors 95 km from the finish, Belgian Philippe Gilbert attacked and opened a 20-second lead.
The 257-kilometer race is also known as the "Hell of the North" because of its treacherous profile including 54.5 kilometers of cobblestones spread out over 29 sectors.
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