Belgian cyclist Michael Goolaerts has died in hospital after suffering a heart attack during Sunday's Paris-Roubaix cycling classic, his team said in a statement.
After the race, Goolaert's Veranda's Willems-Crelan team posted on Twitter, "No update on Michael Goolaerts yet".
"He died of cardiac arrest, all medical assistance was to no avail". No images of the incident itself were available but TV footage of the race showed Goolaerts lying unresponsive on the side of the road as the peloton passed him.
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.
They were the first to try to resuscitate Goolaerts on the scene before the fire brigade and an emergency mobile medical team took over.
"I'm so exhausted after this race", Sagan, the first rider since Frenchman Bernard Hinault to win here as a world champion, said.
Goolaerts rode in support of cyclo-cross world champion Wout van Aert of Belgium. "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.
Paris-Roubaix, also dubbed the "Queen of the Classics", is one of the five Monument classics with Milan-San Remo, the Tour of Flanders, Liege-Bastogne-Liege and the Tour of Lombardy.
The race was marred by several crashes that ended the hopes of outsiders Sebastian Langeveld and Matteo Trentin close to the Trouee d'Arenberg sector. "Our thoughts are with his family and friends".
The 257km race is known as the "Hell of the North", in part because of the numerous crashes its treacherous cobbles provoke. In 2017, almost half of the riders did not make it to the finish in the Roubaix Velodrome.