Tuchel says he could use more additions this months but he would not be drawn on potential names.
"We could use one more central defender, given we play with a back three," said Tuchel. "The profile of the guys in the back three is a little bit different. We are playing with Azpilicueta, who is more of a right-back. We could use one more, let's see what happens.
"We could strengthen our squad with depth but it is one thing what you wish for and one that is possible. We are looking for top quality and competitors on the highest level. You don't always get what you wish for and that is why we are calm and ambitious. Everything is possible until the end.
Asked if he enjoyed working with rumoured target Pierre-Emerick Aubmeyang, of Barcelona, during their time together at Borussia Dortmund, Tuchel said: "I enjoyed a lot working with him. It was a pleasure. Some players stay your players because you were very close and Auba is one of those."