Drinkwater joined Chelsea from Leicester City for a reported £35 million (A$64 million) in 2017 but last played for the London club in the Community Shield in August.
The midfielder was charged with drink driving earlier this week and was left out of Chelsea's squad for their trip to face Slavia Prague in the UEFA Europa League quarter-finals later on Friday (AEST).
"(Drinkwater) has never played because... he's not suitable to my system, to my way of playing," Sarri told reporters.
"Maybe I'm wrong, but it's my opinion. I spoke with him in August, when the market was still open, and said he should look for something different because he wouldn't play. And I told him the reasons, my reasons.
"I don't know (why he decided to stay). Probably he hoped we could change the system. I have a very good relationship with him because, in my opinion, he's a good boy... but he's not suitable for me."
Sarri plans to make five or six changes for the Europa League match and says his side will need to be on their toes to get a result.
"In my opinion, this is a very dangerous match for us," he added. Slavia are a fast team, so we need to be very, very compact and defend really very well.
"They are dangerous, especially on crosses where they attack the box with five or six players, and are dangerous on counter-attacks. So it won't be easy for us."
