At today's Champions League presser for tomorrow's clash with Zenit, Tuchel was asked about the fringe pair.
He said, "If you get registered it's your duty to be ready, you need to be ready here every day when you step on the training pitch, it's the basis.
"Ruben Loftus-Cheek and Malang Sarr is in the squad.
"Now they have to be match ready, I have a feeling that they are, they have a good mentality that's why they'll be on the list or on the bench."
Tuchel was also asked about Ben Chilwell.
He stated: "It's been difficult for him, from a Champions League win, then it was individually for him a tough Euros because he felt he could have played a part for England, Thomas Tuchel said.
"Then to keep training for four or five weeks then he had a personal break which is difficult.
"When I arrived I felt he was mentally tired which is unlucky because Marcos Alonso had a full pre-season.
"We had some talks with him and no further worries with him, he's training and he just needs to be patient. He's in the race now and with a good mental attitude."
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