The 38-year-old, who won the rainbow jersey for the first time in Innsbruck, Austria, last year, won the Vuelta a Espana in 2009, also finishing third in the 2015 the Tour de France and in the 2016 Giro d'Italia.
He also won the oldest of the classic one-day races, Liege-Bastogne-Liege, four times, and the Fleche Wallonne a record five times.
Valverde was given a two-year suspension from the sport in 2010 for his implication in the Operation Puerto blood-doping investigation, even though he never failed a dope test.
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He will take part in the Giro and the Vuelta this year before defending his world title in Yorkshire.
(Reporting by Julien Pretot; Editing by Christian Radnedge)
