World champion Julian Alaphilippe remains in hospital after hitting a tree during Sunday's Liege-Bastogne-Liege one-day race.
The 29-year-old Frenchman suffered two broken ribs, a broken scapula and a collapsed lung.
A huge crash brought down many riders 62km from the finish, with Alaphilippe landing in a ditch.
His Quick-Step Alpha Vinyl team said "a period of further observation" is required before beginning his recovery.
Meanwhile, team-mate Ilan van Wilder has had surgery on the broken jaw he sustained in the same crash.
The 21-year-old Belgian has returned home but has been ruled out of the Giro d'Italia, which starts on 6 May.