Geraint Thomas will race in the Vuelta a Espana, the third and final Grand Tour of 2015 which starts later this month, BBC Wales Sport has learned.
The 29-year-old Welshman will again act as a support rider for Team Sky leader Chris Froome, who confirmed his participation in the race on Monday.
Froome 30, became the first Briton to win the Tour de France twice in July.
Thomas had been tipped as a potential leader for Team Sky if Froome decided not to race.
Froome joins Nairo Quintana of Colombia and Italian Vincenzo Nibali in a strong Vuelta field.
Quintana finished second behind Froome in Paris this year, Nibali was the Tour champion in 2014, while American racer Tejay van Garderen will also compete.
The race starts in Puerto Banus on Saturday, 22 August and finishes three weeks later in Madrid on 13 September.
A Grand Tour refers to one of the three major European professional cycling stage races - the Tour de France, Giro d'Italia and Vuelta a Espana.
The last man to win two in a season was Spaniard Alberto Contador, who won the Giro and Vuelta in 2008.