Asked when he expects a Fabregas replacement - reportedly a straight choice between Zenit St Petersburg midfielder Leandro Paredes and Cagliari star Nicolo Barella - to arrive, Sarri replied: "I have no idea".
Sarri added: "You know very well that Willian is a very important player for us, as I said yesterday in the news conference".
'But I think the character was good and the most important is to win the game.
But, while Sarri will be relieved to see Chelsea remain in control of the race to qualify for the Champions League, this far from convincing performance raised fresh questions about the former Napoli manager's tactics.
"It's very hard to understand". Willian is very important for us so I think it's impossible to lose him in January. We stopped [playing] for 25 minutes.
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Newcastle find themselves in the relegation zone as a result of wins for Southampton and Burnley and another winter of discontent is brewing for the Magpies.
The Magpies' 18 points is their lowest tally after 22 matches of a top-flight season since they were relegated in 1988-89. Today we couldn't do that but we have the quality to do it in the next games.
"We started well but after the goal we slept for 20 minutes, so by the end of the first half we were in trouble", Sarri told BBC Sport.
Florian Lejeune fired a long-range volley through a sea of bodies for Kepa Arrizabalaga to make his first save, while Ayoze Perez sliced wide of the target after latching on to Salomon Rondon's flicked pass.
It was a warning that Sarri's men failed to heed and in the 40th minute Newcastle were level.
With frustration mounting, a misplaced pass by Jorginho triggered angry moans from Chelsea fans, who booed the team off at half-time. The Brazil worldwide received the ball from Eden Hazard and cut in from the left before powering an effort into the back of the net from the edge of the box.