Dembele had less than a season with Tuchel, while with Borussia Dortmund.
The France attacker said, "The coach who impressed me the most? It's Thomas Tuchel.
"He is one of the top three coaches in the world for me with (Zinedine) Zidane and Pep Guardiola. Humanly, the relationship he has with his players is amazing, he is above, there is no better.
"He's the best."