The centre-back has not featured at all for Chelsea this season and gave a positive answer when asked if he could leave when the transfer window reopens, per the Telegraph's John Percy:
"I don't want to jump the gun, but as things stand at this time, probably, yes.
"I'm not a guy who is willing to accept not playing. It's all about playing. Your career's short enough as it is. I've got maximum respect for everybody here at the football club, for the fans and all the players. But sometimes you have to make tough decisions to keep your career going forward.
"As it is now, I’m not really enjoying things. Having been a big part of things for seven years and played a huge part, not just a squad player, I'm definitely finding it difficult this year to deal with that situation.
"The most important thing here is the team, but I've got to look at my situation and my future as well. Everything gradually comes to an end or there's a new challenge around the corner."
Cahill joined Chelsea from Bolton Wanderers in January 2012. He has gone on to win the Premier League, FA Cup, UEFA Champions League and UEFA Europa League during his time at Stamford Bridge.
He did lose his place in the team last season under Antonio Conte. However, he forced his way back into the starting XI and captained the side to an FA Cup victory over Manchester United at Wembley Stadium.
The defender was part of the England squad at the 2018 FIFA World Cup. He told Chelsea TV (h/t Ben Burrows at The Independent), he would be taking a "step back" from international duty after the tournament.
Yet Cahill has been so far unable to force his way into Sarri's thinking. The Italian has preferred David Luiz and Antonio Rudiger as his central defensive partnership.
He brought in Andreas Christensen in place of Luiz for Thursday's Europa League tie against PAOK Salonika, with Cahill an unused substitute.
The 32-year-old is out of contract at Chelsea at the end of the season, but he appears to have accepted he may have to leave the Blues before the end of his current deal.
Freelance journalist Dan Levene said it's the right time for him to depart:
Chelsea may not stand in his way, as they are well-stocked in defence. As well as Luiz, Rudiger and Christensen, Cesar Azpilicueta and 18-year-old Ethan Ampadu can also play at centre-back.
Cahill will turn 33 in December but will still feel he has plenty to offer. He was linked with a move to Turkish side Galatasaray in the summer, according to Fotomac (h/t the Mirror's Jake Polden).
Chelsea may be willing to allow him to leave as he's been a loyal servant to the club. The Blues allowed Petr Cech to depart for Arsenal in 2015 after over a decade of service at Stamford Bridge.