London - Chris Froome -- fresh from wrapping up a Tour de France and Vuelta a Espana double -- believes winning all three Grand Tours in the same year would "take some doing" but "nothing is impossible".
Froome, 32, completed victory in the Vuelta on Sunday to become only the third man to achieve a Tour-Vuelta double in the same year and the first since Bernard Hinault in 1978.
No rider has ever pulled off a Giro-Tour-Vuelta treble and while Froome feels it is unlikely, he does not believe it is unachievable.
"I wouldn't say it's impossible," the British rider, a four-time Tour de France champion, told BBC Radio Four on Monday.
"Nothing's impossible, but certainly it would take some doing."
He was more circumspect about his chances of surpassing Belgian great Eddy Merckx's record of 11 Grand Tour victories.
"A completely different era," said Froome, who finished second in the Vuelta three times (2011, 2014 and 2016) before finally securing the red jersey.
"Eddy Merckx's time of racing, he was able to win every single kind of race on the calendar. The sport has transformed since his time."
Froome's double triumph came after a challenging period for Team Sky.
Bradley Wiggins, Froome's former team-mate, was revealed to have obtained permission to use a powerful corticosteroid before the 2011 and 2012 Tours -- the latter of which he won -- and the 2013 Giro.
Wiggins and team principal Dave Brailsford said the rider's use of the drug, which was sanctioned by cycling's authorities, was necessary for medical reasons.
Sky are also under investigation by UK Anti-Doping over a mysterious package that was delivered to Wiggins during the 2011 Criterium du Dauphine.
Sky deny wrongdoing and when asked if his support for Brailsford was unequivocal, Froome replied: "Certainly."
He added: "For us on the road, we've just been focused on the racing side of things.
"Those allegations haven't been aimed at us at all, so it really hasn't been an issue."