Porte will leave Team Sky at the end of the season to pursue his own leadership goals with a yet-to-be-named team, though the 30-year-old has been heavily linked with BMC.
Froome said he would miss the company of his close friend and regular training partner, who as a super domestique has now been instrumental in helping Sky win three of the past four Tour de France editions.
And the Brit is confident Porte has the potential to realise his dream of a Grand Tour victory.
"Richie is an incredibly talented climber, probably one of the best climbers in the peloton," Froome told the UK's Cycling Weekly.
"There are often occasions where he drops me in the mountains, even in training.
"There is no doubt it. He can ride a very good GC. He has already been a top 10 in the Giro (d'Italia in 2010) as a neo-pro.
"I have no doubt that he has the ability to ride GC in a grand tour."
But Froome said Porte would first need to become more reliable over three-week races.
"Where does he need to improve? Probably in consistency," he said.
"To be able to look at a three-week race (you need) to roll with the bad days as well as the good days."
Porte has enjoyed a lot of success over one-week stage races including winning this year's Paris-Nice, the Volta a Catalunya and Giro del Trentino.
But when stepping up to the grand tours, he has often cracked at vital moments.
After coming second to Froome on the first summit finish at the 2013 Tour to sit second overall, Porte faltered the next day and finished the Tour in 19th overall.
He was pushed up to team leader last year when Froome crashed out of the Tour and despite being second to Vincenzo Nibali after Stage 12, he fell out of contention on the first mountain stage and finished the race 23rd.
This year he also led Sky at the Giro d'Italia, but his race fell apart after a controversial two-minute penalty for accepting a replacement wheel from compatriot and Orica-GreenEDGE rider Simon Clarke.
He eventually abandoned the race because of injuries from a crash.