The 12th stage climbs over the Port de Balès and the Col de Peyresourde to finish at the Peyragudes airport in the Pyrenees.
Froome raced a similar stage to Peyragudes in 2012 when Alejandro Valverde won and Bradley Wiggins rode his way to a Tour de France title.
"It's quite savage. I think there could be rather significant time gaps," Froome said. "Tomorrow is going to be one of the hardest stages in this year's route. It's going to be one of the most important stages of the race.
"I'm hoping it won't be as crazy as the stage we did Sunday [to Chambéry] up in the mountains. A lot of people are going to be trying to use tomorrow's stage to get back in the game."
"I don't want to see any of the guys who have lost time getting back in the game. We are going to work hard to make sure none of the GC guys get up the road early," Froome added.
"The most important thing for us is to keep an eye on Fabio Aru. He is only 18 seconds back. I want to keep my advantage up until the time trial [stage 20]."
The Port de Balès, 11.7 kilometres long, tops out with 30.5 kilometres left in the 214.5 kilometre stage from Pau. The Col de Peyresourde leaves five kilometres to race, including a quick descent and kick to the airport.
"I expect to be in the break and hope to be fighting for the mountains points for this jersey, and maybe try to win the stage," said French climber Warren Barguil (Sunweb), who wears the polka-dot jersey.
"Balès is a big climb, not so easy, but Peyragudes is more rolling at the start and at the end it's getting steep and then we go down again. The last part is pretty hard. We turn left to the airport and it's steep. It's much better for me!"
Simon Yates (Orica-Scott) said: "It's a good opportunity. Any time there is a mountainous terrain there is an opportunity for me to try something. And if there is an opportunity, I'll try."
Yates wears the white jersey of best young rider by 2-58 minutes over Louis Meintjes (UAE Team Emirates). The Brit is 2-02 back from Froome in seventh overall.
Chris Froome's 2017 Tour de France Pinarello Dogma F10
"There are only a few summit finishes in this year's Tour and tomorrow's one of them, so for sure it's going to be very important," Yates continued. "It's also a very long stage, which is very wearing. We've had a lot of long days this Tour, a lot of days over 200 kilometres, and for sure it wears you down."
"The climbs do get harder as the days go on," said Yates's sports director at Orica, Matt White. "The leaders will probably start racing on the last climb of the day.
"The key guys can turn anything into something very difficult. It'll be the mood of the bunch and the tempo that Sky wants to set and how keen they are to try to win a stage. And not letting the major guys move, if they set a certain tempo on a climb, it limits the amount of people who can attack."
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