Nibali told Giro organisers that "the Vuelta is a goal, just like the worlds in Florence."
Nibali won the Giro on Sunday with a dominating performance, having taken his first Grand Tour title at the 2010 Vuelta.
Only three riders have won the Giro and Vuelta in the same year - Eddy Merckx in 1973, Giovanni Battaglin in 1981 and Alberto Contador in 2008. None of them also won the world title in those years.
The Vuelta runs from August 24 to September 15 and the worlds race is on September 29.
Nibali is not planning to ride this year's Tour de France, having finished third last year.