Title contender Nibali crashes out of Lombardy
File picture shows Astana Pro team's Italian rider Vincenzo Nibali competing in the 20th stage of the 68th edition of "La Vuelta" Tour of Spain, a 142.2 kilometres ride from Aviles to Angliru, on September 14, 2013
Nibali was one of several riders, including Spaniards Joaquim Rodriguez and Alejandro Valverde, hoping to finish the European season on a high in the 'Race of the Falling Leaves'.
However the Giro d'Italia champion, who rides for Astana, failed to get back on his bike after a spill which left him limping and with an apparent left knee injury.
Nibali, Rodriguez and Valverde all missed out on victory in the world championships last week when Portugal's Rui Costa triumphed to win the coveted rainbow jersey.
Nibali's abandon comes a day after Britain's Chris Froome, the Tour de France champion, pulled out citing a sore back.
Fellow Italian Michele Scarponi, who had been leading Lampre's bid for victory in the fifth and final 'Monument' of the one-day classics season, abandoned earlier in the race due to illness.