Dier has revived his career after joining Bayern in January from Tottenham.
He said: "He is a fantastic person.
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"He was a very good manager in the Premier League, and he is also a good manager here. I think he is very genuine.
"What you see is what you get, and I appreciate that in a coach. I am extremely grateful that he took me to this great club and gave me this opportunity."
However, it has been a tough couple of years for Dier, who had struggled for minutes at Spurs.
"I have always believed in myself, and I have always believed that I should play at this level.
"I am in the position I am in now because I have always believed in myself. I think I have shown my mental strength."