Defending champion Chris Horner has been forced to withdraw from the Vuelta a Espana just one day before the start due to low cortisol levels. According to UCI rules, he is allowed to start but as his Lampre-Merida team is member of the MPCC, the team has been forced to replace their team leader with Valerio Conti.

Chris Horner won't be at the start line when the Vuelta a Espana kicks off tomorrow. Today Lampre-Merida have announced that the American is out of the race due to low cortisol levels.

Horner has been suffering from a bronchitis since the Tour de France and was given a therapeutic use exemption by the UCI to receive treatment with cortisone. The team suggests that it is the reason for Horner's abnormal cortisol levels.

The UCI rules don't prevent Horner from starting the race but Lampre-Merida is a member of the MPCC and so has to obey to additional rules. They stipulate that a rider has to be withdrawn from competition if the cortisol levels are below a certain minimum.

Dr. Carlo Guardascione, Lampre’s team doctor, explained the situation in further detail in a press release: “After the finish of the Tour de France and after the Tour of Utah, where the athlete was still suffering from bronchitis, Chris Horner underwent two examinations by two specialists for his bronchitis … both specialists agreed that a treatment of cortisone by oral means was the only way to resolve this problem. All the necessary steps were taken to request a TUE, this authorization was given by UCI commission for the athlete to proceed with this therapy on [August 15].

“Physiologically, this treatment can cause a lowering of the cortisol together with other factors such as jet lag after his travel from United States, where he had a time difference of 9 hours.

“After the necessary UCI blood tests were taken, it showed a lower cortisol level compared to the minimum level requested by the MPCC, thus the decision from the team to not allow the athlete to partake in this Vuelta even with having all the necessary UCI authorization in order.”

Horner is hugely disappointed to miss out on his title defence.

“Of course I’m sad about this news," he said. "I was willing to try to defend the 2013 title. [The] Vuelta was my main target in the season, the team signed me with the aim of being competitive in the Spanish race, but I accept the decision linked to the MPCC’s rules. This bad bronchitis caused me a lot of problems, I’ve been suffering from it for weeks and this treatment could have allowed me to solve the problem.

“UCI gave authorization for the treatment, I could race according to UCI rules, but my team is a member of MPCC. I understand it and we all must accept this situation without regrets.”

Horner will be replaced by young Italian climber Valerio Conti.

Last year Theo Bos was withdrawn from the Vuelta on the eve of the race for similar reasons.