Two-time Tour de France champion Tadej Pogacar suffered a broken wrist after crashing out of the Liege-Bastogne-Liege one-day classic.
Pogacar’s UAE Team Emirates said the Slovenian, 24, would need surgery.
“It’s a multiple fracture, so it’ll be complicated for the surgery. It’s too early to speak about the Tour de France,” said UAE Emirates director Mauro Gianetti.
The race was won by Belgian Remco Evenepoel.
He retained his title after victory last year, with Britain’s Tom Pidcock coming second.
The Netherlands’ Demi Vollering had earlier claimed a historic victory in the women’s race.
Pogacar crashed with Dane Mikkel Honore – who also had to pull out of the race – after 85km and was taken to hospital.
UAE Team Emirates medical director Dr Adrian Rotunno said Pogacar had “suffered fractures to the left scaphoid and lunate bones” in the wrist, adding a specialist hand surgeon would be operating on the rider on Sunday.
Liege-Bastogne-Liege was Pogacar’s final race before heading for altitude training for the Tour de France, which begins on 1 July.
After winning this season’s Amstel Gold Race and the Fleche Wallonne, he was the pre-race favourite and had been aiming to become only the third man to complete a hat-trick of Ardennes classic wins.
Davide Rebellin in 2004 and Philippe Gilbert in 2011 are the only other men to complete the trio of wins.
Road race world champion Evenepoel, 23, coasted to victory on the 258km route, the Soudal Quick-Step man breaking away with 30km to go and finishing more than a minute in front of his nearest challengers.
Ineos Grenadier’s Pidcock outsprinted Santiago Buitrago Sanchez of Colombia to claim second place, with Ireland’s Ben Healy just behind them in fourth.
Evenepoel is the first rider to win the race back-to-back since Michele Bartoli in 1998.
Vollering makes history
Vollering’s victory made her only the second woman to complete the hat-trick of Ardennes classic wins.
The 26-year-old’s second Liege-Bastogne-Liege win added to her recent success at the Amstel Gold Race and the Fleche Wallonne.
Compatriot Anna van der Breggen completed the Ardennes triple in the same season in 2017.
“It is unbelievable,” Vollering said. “I felt the pressure as it is not every day you have the chance to do the treble.
“I really wanted to bring home this victory.”
Vollering broke clear from the peloton alongside Italy’s Elisa Longo Borgini with 10km remaining, but the Dutchwoman proved the stronger of the two in the sprint finish.