Hinault was the last rider to pull off the Vuelta and Tour double, in 1978, and he also won the Giro d'Italia three times.
"He has proved that you can win the Tour and the Vuelta in the same year, so why not the Giro?" Hinault told the Guardian.
"What he has managed in Spain is a great thing because the general view was that it was not possible to win either the Giro and Tour or the Tour and Vuelta in the modern era.
"He wasn't as dominant as usual in the Tour, but he's really rediscovered his true capacity at the Vuelta, in spite of having one or two difficult days."
Hinault also argued that it is impossible to establish a hierarchy of the achievements of different cycling greats in the Grand Tours, given that they were racing in very different eras.
Froome has said – most recently on Sunday evening after winning the Vuelta – that he will one day target the Giro d'Italia, but he has not put a specific date on when that might be.
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"Obviously it's very early to say and of course the Giro has come up a few times. I'm not going to say no and over the winter I'll come up with a plan for next year," Froome said.
However, Froome almost immediately qualified that possibility when he pointed out that "a fifth Tour de France victory would be a huge objective for me next year, so I have to keep that in mind."
Froome last raced the Giro d'Italia back in 2010, when he was disqualified on stage 19 to Aprica, when he accepted a tow while trying to get to the feed zone to abandon because of knee pain. He briefly advanced the idea of racing the 2017 Giro d'Italia last year, but commented, as he did again yesterday, that the race route would always have an impact on that decision.
Only six riders have won all three Grand Tours in cycling history, the most recent being Vincenzo Nibali, who completed the hat-trick when he won the Tour in 2014.
