Maurizio Sarri told Danny Drinkwater he was surplus to requirements at Chelsea before the current season even started.
Former Leicester star Drinkwater has not featured at all in a competitive game under head coach Sarri at Chelsea this season, and was arrested on suspicion of drink driving in Cheshire on April 9.
Sarri informed Drinkwater back in August he could not fit into his tactical system and suggested he find a new club – but the England midfielder opted to remain at Stamford Bridge.
"He knows very well he has never played because in my opinion he is not suitable to my system, to my way of playing," said Sarri.
"I told him everything in August. He appreciated it, but he decided to remain, and so he knew very well the situation.
"I spoke with him in August, when the market was still open. I said to him he should look for something different.
"In my opinion, he doesn't play. And I said to him the reasons, my reasons. But, as I said before, he decided to stay at Chelsea."
Asked if Drinkwater is unable to adapt to his "Sarriball" possession style, the Chelsea boss said: "No, I don't think so. It's my opinion. Maybe I am wrong, but it's my opinion.
"I try (to be honest). Of course, sometimes you have to say something different. But in 99 per cent of cases, I try to be honest."
Asked why Drinkwater has stayed, Sarri replied: "I don't know; probably he hoped we could change the system, I think.
"I have a very good relationship with him because, in my opinion, he's a good boy. He's a good player. He's a good player.
"And he's able to play in a 4-4-2 or a 4-2-3-1 very well.
"But he's not suitable for me. He knows this, but I have a good relationship with him.
"I cannot do anything. A player usually wants only to play, nothing else. So I cannot do anything.
"I can only have with him a very good relationship, no more. At the moment, I am not able to satisfy him as a player. So it's very difficult, but he knew."
Chelsea's appeal against a two-window transfer ban relating to recruitment of overseas players aged under 18 will be heard by FIFA on Thursday.
The Blues insisted they were "astonished" by the suspension and still aim to have that embargo overturned.
Chelsea's legal team will attend the hearing in Zurich just hours before the Stamford Bridge men face Slavia Prague in their Europa League quarter-final first leg.
And boss Sarri insisted he will ban any talk of that hearing before the Sinobo Stadium clash against Slavia.
Asked if he would seek updates on the appeal hearing, Sarri said: "Not before the match, for sure.
"We have a club who are very careful about everything, so I don't want to talk about this.
"We are here for the Europa League, a very important target for us, and I want my players to think only about the Europa League."
