Paris - Spain's former Olympic road race champion, Samuel Sanchez, has failed an out-of-competition doping test, cycling's governing body the UCI announced on Thursday.
The body said Sanchez had tested positive for growth hormone releasing peptides in a sample taken on August 9 by the Cycling Anti-Doping Foundation.
"The rider has the right to request and attend the analysis of the B sample. In accordance with UCI Anti-Doping Rules, the rider has been provisionally suspended until the adjudication of the affair," the UCI statement said.
Now 39, Sanchez is best known for winning gold in the road race at the 2008 Olympics in Beijing.
Twice a podium finisher in the Vuelta, the BMC team rider had been due to take part in this year's race, which begins in the French city of Nimes on Saturday.
A BMC team statement said: "All riders and staff are held to the highest ethical standard and BMC Racing Team is extremely disappointed to share this news on the eve of the Vuelta a Espana."
They have replaced Sanchez with Belgium's Loic Vliegen for the three-week race.