Lance Armstrong, middle, rides during the first stage of the Vuelta of Castilla and Leon race in Spain. Armstrong was taken to a hospital after falling. (Victor R. Caivano/Associated Press)

Lance Armstrong fractured his collarbone Monday during a race in Spain and will require surgery, leaving in question his participation in the Tour de France in July.

"We'll go from there," said the seven-time Tour champion. "I think for the Tour it's a very big problem."

Armstrong will fly back to the United States after being knocked out of the first stage of the Vuelta of Castilla and Leon stage race in Spain.

"The crash has put my upcoming calendar in jeopardy, but the most important thing for me right now is to get back home and rest up and begin my rehab," the American cyclist said in a statement Monday.

Armstrong is scheduled to compete in the Giro d'Italia from May 9-May 31. The Tour runs July 4-26.

The 37-year-old American said he had "been lucky to avoid one of the most common cycling injuries" in his 17-year career.

Armstrong was tossed off his bike during a pileup about 20 kilometres from the finish line and was taken to hospital by ambulance. He was grimacing and trying to hold his right arm as he entered the ambulance.

Armstrong said the crash was no one's fault.

"Toward the end of the race people started getting excited, a bit of wind, some hills and everybody wanting to be at the front," he said. "A couple of guys crashed in front of me, I crossed my wheel, then I hit them and over the top."

"The collarbone is broken, and I have a little bit of road-rash abrasions," Armstrong said as he left Valladolid University Hospital. "I've never had this happen before; it's pretty painful. I feel really miserable."

Astana team leader Johan Bruyneel said on his Twitter feed that there were no complications in the break, and suggested Armstrong could be back riding soon.

"Clean collarbone fracture," Bruyneel said. "Should be fast recovery."

After falling off his bike, Armstrong sat in the grass beside the road, his right shoulder slumped and his wrist resting on his right thigh. When help arrived, he motioned toward his right shoulder. Armstrong eventually walked to the ambulance and climbed into the back.

Astana teammate Levi Leipheimer described the pileup on his Twitter feed.

"Lance was involved in a huge crash as the road narrowed and became very rough," Leipheimer wrote. "He wasn't far from the front, as he was riding top 10 all day."

Armstrong said the crash was no one's fault.

"Toward the end of the race people started getting excited, a bit of wind, some hills and everybody wanting to be at the front," he said. "A couple of guys crashed in front of me, I crossed my wheel, then I hit them and over the top."

After first being taken to the Rio Carrion hospital in Palencia, Armstrong was taken to the hospital in Valladolid.

Armstrong won seven straight Tours from 1999-2005 before retiring. He returned after 3 1/2 years, and was hoping for another triumphant ride through Paris. The Vuelta of Castilla and Leon race was Armstrong's first stage race in Europe since winning the 2005 Tour.

Astana team leader Johan Bruyneel said on his Twitter feed there were no complications in the break, and suggested Armstrong could be riding soon.

"Clean collarbone fracture," Bruyneel said. "Should be fast recovery."

Added Astana spokesman Philippe Maertens: "We are confident he can still race the Tour de France, of course. He will be off the bike, but he can still do condition training."

Armstrong started his comeback at the Tour Down Under in Australia in January, where he finished 29th overall, 49 seconds behind winner Allan Davis of Australia. He then finished seventh in the Tour of California in February.

On Saturday, Armstrong raced in the Milan-San Remo cycling classic and finished 125th, 8 minutes, 19 seconds behind winner Mark Cavendish.

The mainly flat first stage of the Castilla and Leon covered 175 kilometres from Paredes de Nava to Baltanas. It was won by Joaquin Sobrino Martinez of Burgos Monumental in 4 hours, 31 minutes, 53 seconds after a sprint finish. He was followed by David Vitoria of Rock Racing and Jose Joaquin Rojas of Caisse d'Epargne.