Defending champion Chris Horner will miss the Vuelta a Espana because of an abnormally low cortisol level.
Horner was given therapeutic exemption by cycling's governing body, the UCI, to use oral cortisone to treat bronchitis, but the American was withdrawn by his Lampre-Merida team.
Hs cortisol level is not illegal, but it is below that specified by the Movement for Credible Cycling (MPCC).
"It has been necessary for a change of programme," the team said.
In its statement, Lampre-Merida added: "Even though Horner would be allowed to start the race as far as the UCI is concerned, the team are obliged to respect the rules and regulations of the MPCC organisation in a completely voluntary decision."
The American made history last year when he won the Vuelta at age 41, becoming the oldest ever winner of a Grand Tour.