Nairo Quintana has elected not to ride in the Vuelta a Espana, with his decision coming a day before the start of the season's final Grand Tour gets under way in the Netherlands.
On Wednesday, Quintana was retrospectively disqualified from this year's Tour de France for an in-competition drug infringement.
The Colombian finished sixth in the General Classification, his first top-10 Grand Tour finish since the 2019 Vuelta and his best performance in the Tour de France since 2016.
However, the UCI announced that two samples of Quintana's blood showed traces of tramadol, a banned substance.
The 32-year-old was given 10 days to appeal the ruling with the Court of Arbitration for Sport (CAS), though he has not been banned from competition as it is a first offence.
On Thursday, the Colombian confirmed he would not be riding in the Vuelta, despite initially stating he would be doing so.
In a widely reported statement, Arkea-Samsic rider Quintana said: "I communicate that I will not participate in the Vuelta to assert my reasons before the Court of Arbitration for Sport, I will return to the calendar races at the end of the season."
Quintana had responded to the allegations via his social media channels, stating: "I have been surprised by the announcement of the UCI of an infraction for use of tramadol.
"I am completely unaware of the use of this substance and I deny having used it in my career.
"With my team of lawyers we are exhausting all the processes to assume my defence.
"I also want to ratify that I will be in the Vuelta a Espana, riding my best for the team, my country and my fans."