The Spanish tour races up to 1830 metres for the stage 14 finish to Sierra de La Pandera on Saturday and 2510 metres on stage 15 to Sierra Nevada.
"An off-day could happen with anybody," said Sky's Gianni Moscon. "Vincenzo Nibali, Alberto Contador and Esteban Chaves, and whoever else could try, but for sure, Chris is the man to beat! They know that too. And we aren't afraid of anyone."
Sky has protected Froome's lead since he took it on stage three in Andorra. He was last tested with the summit finish to Calar Alto and with the stage 12 crash on Thursday.
"It's very hard to say what's going to happen in this Vuelta, as we saw yesterday, anything can happen," Froome said.
"Sunday's stage is going to be very hard again, up to 2500 metres at the end of a very tough stage, as well. We are going to see some big time gaps."
Froome had a bloody right knee and left elbow on Friday from his crash on stage 12. He said the area around his hips hurts the most.
"Before yesterday, I would've said yes, [Froome would cement his lead this weekend], but I don't know what kind of impact the crash had on him," Dutchman Steven Kruijswijk (LottoNL-Jumbo) said wearing an ice-vest after stage 13.
"You still have the third week coming up and he's done the Tour and won. It'll be hard to say until the last day how he will do."
On Sunday, they climb the Alto de Hazallanas and the final 19.3-kilometre haul up Sierra Nevada – all within 129 kilometres. Last year, Froome lost his chance to win the Vuelta on a short 101-kilometre stage to Formigal.
"Tomorrow, it's only the last climb where we have to fight, but the stage Sunday is a short stage and should be explosive and interesting. Normally Vincenzo Nibali and Alberto Contador will take the chance."
Froome leads the race overall with 59 seconds on Vincenzo Nibali (Bahrain-Merida) and 2-13 minutes on Esteban Chaves (Orica-Scott). Contador has more time to make up, sitting ninth at 3-13.
Contador said, "Of these two stages that come, one is more explosive, La Pandera, and in the other, if you have a bad day you can completely lose all possibility, not only the podium, but even not finishing among the first 10, because it is a very long climb that goes up to 2500 meters.
"There are always brave people who are encouraged to attack, but hey, we will go day by day."
"These are long and hard climbs," said Quick-Step sports director Rik Van Slycke. He looks after David De La Cruz, who sits fifth overall.
"Sunday is a short stage. They made it so short because they want it to be a show, and cycling fans will enjoy the day.
"Expect an aggressive Nibali because he also has a good team. Fabio Aru is not 100 per cent and things can change quickly. And if you suffer a lot in the beginning the Vuelta you get the bill later.
"David is going better, you saw that when he chased back after his bike problem on Calar Alto."
Unlike the Tour de France climbs, Froome has not previewed most the Vuelta a España climbs in training.
"They are climbs that I've not seen before," he explained. "I have to rely on David Lopez and Mikel Nieve, who have seen them and know what we can expect.
"Otherwise, I always put my faith in our sports director, Nicolas Portal. He gives us all the info on all the climbs as we approach them on the road and in the mornings in the meetings.
"It's different when you haven't seen them and you can't visual them. It is different in this Vuelta, not like the Tour, I haven't seen these climbs.
"It is different, but at the same time, I have faith in the guys like Nicolas Portal to let me know exactly what's coming up."
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