Veranda's Willems-Crelan rider Michael Goolaerts has died after suffering a cardiac arrest during the 2018 edition of Paris-Roubaix.
After the race, Goolaert's Veranda's Willems-Crelan team posted on Twitter, "No update on Michael Goolaerts yet".
It added that he "died of cardiac arrest, all medical assistance was to no avail".
He has been in superb form this season - placing ninth at Dwars dooor Vlaanderern and 20th at both Driedaagse De Panne and Kuuren-Brussel-Kuurne.
Goolaerts had been airlifted to hospital after collapsing about 150 kilometres (93 miles) from the finish.
However, Sagan's win was overshadowed by a crash involving the Belgian rider Michael Goolaerts, who was taken to a hospital after receiving CPR treatment on the side of the road.
"I avoided crashes, and, actually, I feel less exhausted than the previous years", Sagan, the first rider since Frenchman Bernard Hinault to win here as a world champion, said.
Paris-Roubaix is one of the five Monument classics with Milan-San Remo, the Tour of Flanders, Liege-Bastogne-Liege and the Tour of Lombardy.
In sunny and warm conditions in northern France, the triple world champion, who rides for Bora-Hansgrohe, broke clear of the main pack in pursuit of the three riders who remained from the group of nine that had taken an early lead with 200km remaining.
"It's wonderful to win Paris-Roubaix".
"It's very good for my career, when I was younger I dreamed of winning this race".
Shortly after the 257-km race ended, Paris-Roubaix director Christian Prudhomme told Reuters that Goolaerts had to undergo a scan at the Lille hospital. "I attacked at the right moment and I kept going until the finish".
The incident happened at a part of the course known as "Hell of the North".