American cyclist Lance Armstrong fractured his right collarbone in a crash during a race on Monday.
His Astana team said he might require surgery on the injury sustained during the first stage of Spain's Vuelta Castilla y Leon.
The 37-year-old fell along with several other riders about 20 km from the finish line of the Paredes de Nava to Baltanas leg and was taken away in an ambulance.
The injury has thrown into doubt his plans to ride in the Giro d'Italia in May. Armstrong will make an announcement at a later date on whether he will compete in the Italian three-week stage race.
Armstrong, a cancer survivor who went on to claim a record seven Tour de France crowns, ended a three-and-a-half year retirement at the Tour Down Under in Australia in January.
He declared his goal this year is to win an eighth Tour de France title in July.
Astana team manager Johan Bruyneel said the injury was a clean fracture without complications and he should make "fast recovery," an indication that he could be able to compete in the Tour de France.
The cyclist will return home to the States where a decision will be made on whether surgery is needed.