Sassuolo sports chief Giovanni Carnevali says the club has accepted Francesco Magnanelli's departure.
The assistant coach has left to join Max Allegri's backroom team at Juventus.
Carnevali said: "The historic captain began his journey with Alessio Dionisi and now has made a choice that distanced him from our colors.
"I hope he can find the continuity necessary to grow in the best possible way.
"Though I think another year with us would have done him good."