Cesc Fabregas played under Maurizio Sarri before leaving to join Monaco in January after slipping down the pecking order at Stamford Bridge.
Despite guiding Chelsea to Europa League glory and third in the Premier League in his first season at Stamford Bridge, Sarri is expected to leave Chelsea this week for Juventus.
Fabregas has described Sarri as very superstitious and very stubborn.
“He is very superstitious, he is very stubborn in this way,” Fabregas said, according to Daily Mirror.
“He is a manager with his own ideas and he doesn’t move from them much.
“He has an idea of how he wants to play and the football that he really wants to play. He doesn’t move from it. No matter what you tell him, no matter what you advise him, no matter what your opinion is, he will never change.
“But he did it the way he likes it. He has his own vision of football and, in the end, he is where he is with it and you have to respect that.”
Chelsea legend Frank Lampard is being considered as replacement for Sarri and Fabregas has been impressed with his first season in management at Derby.
“I think he has done a really impressive job. It’s his first ever job. He changed many things,” Fabregas added.
“I saw him in Russia with the BBC and he had a very difficult squad, an older squad full of players at the end of their contracts as well.
“He renewed completely the squad, took on young players.
“He played a really aggressive style, attacking football. Really for a first ever job, I think he has done really good.”