Even without the unique start, the stage is expected to be one of the most explosive in the 2018 Tour de France at only 65 kilometres.
"I think certainly there will be some attacks, but I'm not so sure the grid start will affect the race to much," Thomas said.
"If some guys in the top-10 go that will be a gutsy move. There are a few guys who you might expect to go more than others.
"Like I say, there's such a lot of climbing over a short period, that final climb as well. To go from the start would be risky, for sure plenty of guys are maybe wiling to take that risk. We have to ride it cleverly and ride it together."
Thomas has led the race since the Alpine stages, where he won two summit finishes to La Rosèire and Alpe d'Huez. Behind, Sky team-mate Chris Froome sits second overall at 1-39 minutes and Tom Dumoulin (Sunweb) third at 1-50.
The stage is the shortest road stage in the last 30 years of the Tour and an overall fight is expected with Paris less than a week away. Of the 65 kilometres, 43 of those will be spent climbing.
The 1996 Tour featured a 46-kilometre stage, shortened to that length due to bad weather. This is the shortest planned stage since a split one in 1985.
The stage also features no neutralised zone ahead of kilometre zero. At the start line, kilometre zero, the riders will be placed in the same order as the general classification. They will be in five different groups. The first 20 riders will be in the first group, offset in rows with Thomas first.
Even without the grid start, it could be "massively decisive" in the final overall outcome of the 2018 race.
"The stage is going to be massively decisive, there could be big gaps. It's the first time we've ever done a stage like that, there's a good two hours of climbing which is a lot over such a short period of time," Thomas said after stage 16 in Bagnères-de-Luchon.
"Maybe there weren't as many attacks today because everyone is apprehensive about it. We've got to be clever with it, we can't get carried away at the start. The final climb is possibly the toughest climb of the Tour. It's a big, big day and for sure there are going to be some splits."
The stage travels through the Pyrenees, staring in Bagnères-de-Luchon, covering the Col de Peyresourde and the Val Louron-Azet before finishing up the Col du Portet.
"We possibly need to treat the stage like a time trial. I guess in a TT you wouldn't want to go out too hard and it's the same tomorrow," continued Thomas.
"On that final climb anything can happen. There's a lot of climbing to that point, and the race has been super hard to this point. We [Thomas and Froome] may find ourselves together having to chase or together in front. There could be big gaps, there are so many different scenarios. But like I said, as long as me and Froome don't race against each other, that's the main thing."
Making the stage more dangerous for the overall race, the forecast predicts rain for the final climb.
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