The 22-year-old defender penned a new contract on Thursday, keeping him at Stamford Bridge until 2026.
"His consistency [has impressed me]. He can produce the same performances in different games at this young age," said Tuchel. "It's a new challenge for him to be now a regular player for Chelsea.
"He was very strong in pre-season, showed no nerves in the pre-season games and when it came to the first start, he played in Super Cup. That was impressive because he did what he did in the friendlies. This is what I like a lot about him.
"He's doing his thing and he is not affected in the moment by too much praise or by the pressure that can arise with spectators.
"He can still and needs to improve in his things. The level he can provide is very high, I'm super happy. He is a calm guy, very focused and knows what he wants.
"He was never hiding that this was his dream, to play here in blue at Stamford Bridge.
"It's how he behaves, if he continues to stay that humble with both feet on the ground and living up to his dream by actually living up to it then he's on a good road."
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