Valladolid, Spain  - Lance Armstrong broke his right collarbone when he fell Monday in the first stage of the Vuelta of Castilla and Leon cycling race, the race's organizers confirmed.

The US cycling legend, 37, underwent tests at the Hospital Clinico in the northwestern Spanish city of Valladolid, but was set to leave hospital later Monday, after receiving treatment and painkillers to alleviate his condition, organizers added.

Armstrong - the winner of a record seven editions of the Tour de France - withdrew from the race some 20 kilometres before the stage finish in Baltanas, after being involved in a multiple fall.

He initially sat on the ground for several minutes, visibly suffering pain to his right arm. An ambulance later took him to hospital in the nearby city of Valladolid.

This was the first race in which the US cyclist was set to compete with the Spaniard Alberto Contador. Both are in the same team, Astana, and are fighting for team leadership.

"There's no way I can come back after four years and reclaim leadership or reclaim some type of ownership. I have to respect the current results and he's the best right now. And until that changes, he's the leader," Armstrong said Monday, before the start of the race.

"It doesn't feel as if there is a problem," he stressed. "I think there is a perception that there should be a problem but I don't think we feel that."

The modest Vuelta of Castilla and Leon had attracted over 100 journalists - four times more than usual - over the Texan's presence.

Armstrong returned to racing this season, three-and-a-half years after he retired from professional cycling. He has already raced in the Tour Down Under, the Tour of California and the classic Milan-San Remo, and he was planning to compete in the Giro d'Italia in May.

The stage was eventually won by the Spaniard Joaquin Sobrino Martinez, of the team Burgos Monumental. (dpa)