Armstrong suffered the injury on the first stage of the Vuelta
Seven-time Tour de France champion Lance Armstrong underwent surgery on his broken collarbone on Wednesday.
Armstrong had a stainless steel plate and 12 screws inserted to stabilise his right collarbone, which was broken in four places.
The 37-year-old fell off his bike during the Vuelta Castilla y Leon in Spain on Monday.
"This was a challenge. It was a hard case," said surgeon Doug Elenz, who performed the operation in Texas.
Elenz said Armstrong could be able to resume light training after a week, but it would take between eight and 12 weeks to heal fully.
Prior to the operation, Armstrong was confident of being fit to make his racing comeback in May's Giro d'Italia as part of preparation for a return to the Tour de France in July.
"I think the Giro is still very do-able," he said. "It's the biggest setback I've ever had in my cycling career, so it's a new experience for me.
"The scan showed the clavicle in quite a few more pieces than we originally thought," added Armstrong.
"There will definitely be a plate placed on the top of the clavicle so he [Elenz] can anatomically put all this stuff back together."
He added: "It's a very common cycling injury. You hear of guys who race two weeks later, you hear of guys who race two months later."
Astana team manager Johan Bruyneel said he did not believe the injury would affect Armstrong's chances of an unprecedented eighth Tour de France title.
But the Belgian said that, in his opinion, the injury has put an end to any prospects of him winning the Giro.
"A broken collarbone in the month of March does not at all compromise the start of the Tour de France or your performance in the Tour de France," said Bruyneel.
"But he has to have at least a decent level to be in the race and to compete at a certain level.
"Now it's almost clear that he's not going to be able to be a contender but we just have to change our focus and try to do the Giro, if he can get to the start, with another mentality."