"Armstrong suffered a fracture of the third medio of the right clavicle," the race organizers said after he had an X-ray at a hospital in the Spanish city of Valladolid.
"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."
Most riders need about four weeks off the bicycle to recover from a broken collarbone. That would restrict Armstrong's training for the three-week Giro d'Italia, which starts May 9, and for his main goal, the Tour de France, which starts July 4.
"I think for the Tour, it's a very big problem," the Texan said when he left the hospital.
Armstrong, 37, was grimacing and holding his right shoulder as he was put into an ambulance after the crash during the Vuelta a Castilla y León.
He went down with about a dozen other riders on the first stage of the five-day race northwest of Madrid. As the others got back on their bicycles and sped off, Armstrong remained seated on the ground at the side of the road until help arrived.
He appeared to be the only rider seriously hurt.
Seven consecutive times the winner of the Tour de France, the Texan ended three years of retirement this winter by returning to races, first in Australia and then in the Tour of California. He rode most recently Saturday in the Milan-San Remo classic in Italy, finishing far back and looking less at ease than he did from 1999 through 2005, when he dominated the Tour de France.
In the Spanish race, he was near the back of the pack as it traveled on a road in poor condition about 15 kilometers, or 10 miles, from the finish.
An American teammate, Levi Leipheimer, told VeloNews, a Web site, that he did not see the crash but that "It was on really narrow, bumpy roads. It was a pretty bad road, super-rough and narrow. The edges were deteriorating, with cracks and parts missing."
Just moments before, the race, as seen on television, had passed over smooth macadam. With the transition to a back-country surface, it appeared that some riders had clipped each other's wheels, causing the mass crash.
In his schedule for both the Giro and the Tour, Armstrong had not been penciled into the Vuelta a Castilla y León, but his program was changed because the race includes a time trial and two mountaintop finishes, both good preparation for the grand Tours.
In addition, it offered a chance to ride with his teammate, Alberto Contador, who won the Tour in 2007, while Armstrong was retired, and the Giro and Vuelta a España, the two other major long races, last year. Contador is also the defending champion in Castilla y León.
At age 26, Contador, a Spaniard, has never ridden with his Astana teammate Armstrong.
Their goals are similar victory in the Tour and a rivalry between them has become inevitable although both deny it.
To ensure that they did not compete before the Tour to determine who would be the team leader there and who would be a support rider, their schedules this spring were arranged to avoid confrontation.
Only a change early this month brought Armstrong into the Spanish race where he crashed Monday.
The Texan appeared to be critical of Contador a few weeks ago when the Spaniard lost a big lead in the Paris-Nice race and finished fourth.
"He's a big talent, but he still has a lot to learn," Armstrong said.
He added that Contador had to learn to use his team better.
That was one of his goals in entering Castilla y León, Armstrong explained to help Contador learn to be a strong leader. The Spaniard, who has brushed off any implication of rivalry, had no immediate comment on Armstrong's injury.
The Texan has been wary of predicting victory in the coming Tour. In a news conference before Milan-San Remo on Saturday, he said that his return as winner was not guaranteed.
He explained that he was confident he would attain a high level by July, but admitted that he could take for granted he would be the same rider he was.
"It's hard to say," he confessed. "In the past, I was always riding to win. We're not there yet. Frankly, I don't know if I will get back there.
"This experiment, if you want to call it that, has never been attempted before. Would I like to be? Yes, I'd like to be competitive.
"There are no guarantees," he continued. "Before, there were question marks each year, whether I was early or late in condition. The question mark is a bigger one now.
"We have nothing to compare it to. No one's ever come back from nearly four years and won again, no one who's almost 38 has done this before."
The broken collarbone now makes it seem even more unlikely.
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