Reigning Tour de France champion Jonas Vingegaard suffered a collapsed lung in Thursday’s crash in the Itzulia Basque Country race.
The 27-year-old Dane broke his collarbone and several ribs in a high-speed crash on a descent on stage four.
His team, Visma-Lease a Bike, said on Friday that hospital tests also revealed bruising or bleeding of the lung tissue.
They said: “He is stable and had a good night. He remains in hospital.”
Race leader Primoz Roglic and fellow Grand Tour winner Remco Evenepoel also abandoned the race after going down in the crash.
The remaining 35km of the stage were neutralised.
Wout van Aert, Vingegaard’s leading domestique and winner of nine stages of the Tour, broke his collarbone and several ribs in a crash at the Dwars door Vlaanderen one-day race on 27 March.
This year’s Tour de France starts on 29 June.