The 31-year-old's contract expires at the end of the season, with British media reporting the player is close to securing a move to AS Monaco this month.
"I don't know if he is able to play tomorrow because in the last match he had cramp in the calf so he needs to rest I think," Sarri told reporters ahead of Chelsea's League Cup semi-final first-leg clash against Tottenham Hotspur on Tuesday.
"Yesterday he had a free day for the injury but I don't know (if he is going to Monaco). I can say only my opinion, I don't know the decision of the club. In my opinion he needs to go."
Fabregas, who has won two Premier League titles since joining Chelsea in 2014, has struggled for first-team opportunities under Sarri, making six appearances in the league this season.
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"You know very well the situation and in our club there is a rule, the renewal for players over 30 is usually for a year," Sarri added.
"He has an offer for two years and I don't want a very important player like Cesc to be unhappy."
Sarri ruled out Ruben Loftus-Cheek from the Spurs clash at Wembley Stadium after the midfielder was substituted against Forest with a back injury.
The Italian coach said the club will look to boost their midfield options if Fabregas leaves this month.
"Now with the midfield we are in trouble because I don't know about the situation with Loftus-Cheek, if it's serious or not," Sarri added.
"Without Cesc we only have five so we need a replacement."
(Reporting by Hardik Vyas in Bengaluru; Editing by Christian Radnedge)
