Kai Havertz says he played his best football at Chelsea under Thomas Tuchel.
The former Blues manager was named Bayern Munich coach on Friday.
Havertz told Kicker: "I am very grateful to Thomas Tuchel. We had a really good relationship at Chelsea.
"I had a hard time with football at the start of my Chelsea career, but then a German coach came along who turned everything upside down.
"He definitely made me a better player. He taught us that every little detail is important in football.
"No matter how well you played, you were told if you made a bad pass.
"It helped me a lot at the time, even though I went crazy inside when he said negative things, but when I look back, it was absolutely perfect for me."