Ziyech’s future has been in doubt, with AC Milan monitoring his situation after he was reduced to a fringe role under Tuchel last season.
But the Morocco winger has impressed Chelsea’s manager with his performances in pre-season and it is believed he could strike up a lethal partnership with £97.5million signing Romelu Lukaku.
Tuchel has an embarrassment of riches when it comes to forward options, with Ziyech, Mason Mount, Kai Havertz, Timo Werner, Christian Pulisic and Callum Hudson-Odoi all fighting for one of the two roles either side of Lukaku.
Ziyech, who endured an injury-disrupted campaign last season, faces a battle for regular game-time, but Tuchel believes he could be a key player.
He said: “Any partnership could be very promising when Hakim plays on a high level. On his level.
“I think he was very promising in pre-season. He had some very good matches last season, also some difficulties and hard decisions from me to take. But the pre-season was very promising and pretty impressive from him.
“The attitude which he arrived here was absolutely the right attitude to grow and to show personality. This is what he did. He was fantastic from day one. He was decisive in every single friendly game we played and he was decisive in the first competitive game, the [Super Cup] final against Villarreal.”
Ziyech is in contention to feature against Arsenal on Sunday after recovering from a shoulder injury suffered in the Super Cup. But Tuchel insists he will not take any risks.
He added: “Very unfortunately he got injured so now we need to take care of it because on one side we are very happy he is back on the pitch, on the other a shoulder injury can be a bit tricky.
“Tomorrow [Saturday] is decisive for him. We will see how far it can go. With a shoulder injury you can still run and keep your fitness so you don’t lose too much of that.
“Once he gets the green light and feels totally free hopefully he can find his performance from this season very quickly because he is very important for us.”
Chalobah has also impressed Tuchel, who has told the defender he will be incorporated into the first-team squad, rather than go out on loan.
“I think he did a fantastic pre-season with us,” added the German. “He’s a very good player and even more important, a top character.
“He has both feet on the ground, he took his chance very impressively. He played very good matches in pre-season, he performed for 120 minutes against Villareal and then another strong 90 minutes against Crystal Palace. So now I think it’s very logical that he stays with us, and he’s looking for his chance here.
“We let some players go but Trevoh is a guy we absolutely want to keep, and this is the status for him.
“We had a talk yesterday, and I think his situation was he went out on loans, he had the loans he needed to develop, but now is a good moment to stay with us and be a part of the group. And to take further steps towards fulfilling his dream which is to be part of a strong Chelsea squad, which he is at the moment.
“And we trust him. He deserves it, this is not a gift, this is what he deserves for now.”