(CNN) -- Champion cyclist Lance Armstrong returned to the United States on Tuesday, a day after breaking his collarbone in a fall during a comeback race in Spain, he said via Twitter.
Lance Armstrong is loaded onto an ambulance after crash in the Vuelta Ciclista a Castilla y Leon race Monday.
"Back in the good ol' U S of A," he wrote, or "tweeted" -- as sending short messages on the Web site is known.
Armstrong, the only cyclist to win the Tour de France seven times, will see doctors in the United States to determine whether he needs surgery.
Emerging from a hospital with his arm in a sling Monday, Armstrong said he was "miserable."
"I just need to relax a couple of days and then make a plan," he said.
Armstrong, riding for Team Astana, crashed about 16 kilometers (10 miles) from the end of the first stage of the five-day Vuelta Ciclista a Castilla y Leon race. He said he had never broken a collarbone in his 17 years as professional.
"It's pretty painful," he said. "Just wait and see how it heals."
The crash took down several riders but Armstrong appeared to be the only one injured.
"That's cycling," he said. "It's nobody's fault. Crashes happen all the time."
As they came within a few miles of the finish, Armstrong said, racers started picking up speed and jockeying for position.
"It happens quick when it happens," he said. "It could have been worse."
Armstrong could be out three to four weeks, said Jacinto Vidarte, spokesman for the five-day race. Watch Lance Armstrong speak after injury »
Armstrong, who is attempting a second comeback after retiring in 2005, was planning to race May 9-31 in the Giro d'Italia, one of Europe's most prestigious and grueling stage races. He said Monday his plans for racing in the Giro are now "problematic."
Armstrong's first comeback came in 1998, two years after he was diagnosed with advanced testicular cancer that had spread to his lungs and brain. Doctors gave him a less than 50 percent chance of survival.
Armstrong, 37, announced he was coming out of retirement last year and was using the Spanish race as a warm-up for the Tour de France.
CNN Madrid Bureau Chief Al Goodman contributed to this report.