Froome, 28, has never won one of the cycling's big three events, but starts the 100th running of the Tour de France on Saturday as the clear favourite to win the famous yellow jersey.
Froome's rise seems rapid on the surface, but there were signs he was at least as strong as last year's winner Sir Bradley Wiggins - absent this year with a knee injury - as he played a supporting role and took second place.
Before that, he had finished second, ahead of Wiggins, at the 2011 Vuelta a Espana.
"If you look at Chris's season last year and even the Vuelta in 2011, he's been at a pretty good level," Porte said.
"He was sick at the start of last season (Froome suffered from the draining tropical disease bilharzia) and that suppressed him a bit, but this year he has been healthy and so motivated.
"He knows after last year he can win and could be the next general classification rider of his generation.
"I think that motivates the guy. You see him outside of riding and he's a normal guy, but then he goes into race mode and it's impressive to watch."
If Froome was Wiggins' chief lieutenant last year, that job is now Porte's.
Although there is expected to be no let-up in the metronomic pace Team Sky are known for, it is a much-changed line-up from last year with five new riders - including British Tour debutants Peter Kennaugh and Ian Stannard - in the nine-man squad.
"It's a different team, it's a different Tour," said Porte. "It's not like a car where you can just compare horsepower.
"In the climbing last year we were good, but hopefully this year we will be better. Geraint Thomas and Peter Kennaugh are climbing really well.
"You can't replace Bradley Wiggins but other guys are going to step up."
Porte is a close friend of Froome's as well as being a former team-mate of his main rival this year, Alberto Contador.
However, he insists friendships do not affect the way he will approach his job.
"I was pretty close to Bradley as well, but closer to those two than I was to Alberto," he said.
"But I don't think it makes much difference here. You do your job. Yes, Chris and I ride together most days, but you just have to get on with it."