Samuel Sanchez, who had been due to start the Vuelta on Saturday as part of BMC Racing's team for the Spanish Grand Tour, has been provisionally suspended after failing an anti-doping control.
The team said that it had provisionally suspended the 39-year-old, winner of the Olympic road race in 2008 and of stages at the Tour de France and Vuelta.
"In accordance with BMC Racing Team’s zero tolerance policy and UCI regulation, Sanchez has been provisionally suspended with immediate effect," it said.
"Until the results of the B sample are provided, no further action will be taken."
The UCI WorldTiur team added: "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 España. Loïc Vliegen will replace Sanchez at the Vuelta a España."
In a statement, the UCI said that he had been"notified of an Adverse Analytical Finding (AAF) of GHRP-2* in a sample collected in the scope of out-of-competition control on 9 August 2017.
"The doping control was planned and carried out by the Cycling Anti-Doping Foundation (CADF), the independent body mandated by the UCI, in charge of defining and implementing the anti-doping strategy in cycling.
"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.
"At this stage of the procedure, the UCI will not comment any further on any of these matters," the UCI added.
According to the UCI, "GH-Releasing Peptides (GHRPs) are classified as 'Peptide Hormones, Growth Factors, Related Substances and Mimetics' as per the World Anti-Doping Prohibited List 2017."
Born in Scotland, Simon moved to London aged seven and now lives in the Oxfordshire Cotswolds with his miniature schnauzer, Elodie. He fell in love with cycling one Saturday morning in 1994 while living in Italy when Milan-San Remo went past his front door. A daily cycle commuter in London back before riding to work started to boom, he's been news editor at road.cc since 2009. Handily for work, he speaks French and Italian. He doesn't get to ride his Colnago as often as he'd like, and freely admits he's much more adept at cooking than fettling with bikes.