Vincent Aboubakar, Rachid Ghezzal, Jean Onana and Valentin Rosier have also been dropped.

Besiktas said the decision was made because of "poor performance" and "incompatibilities within the team".

"Our work regarding recruitment for the new squad structure continues," the club added.

Bailly, who was at Old Trafford from 2016 to 2023, has only made eight appearance for Besiktas.

It is understood the players' contracts have not been cancelled but they have been removed from the first team and made to train away from the squad for the foreseeable future.

Besiktas, managed by Riza Calimbay, sit fifth in their domestic league, 14 points behind top two Fenerbahce and Galatasaray after 15 games of the season.

They have also been knocked out of the Europa Conference League and are bottom of their group after four defeats in five matches.

"Our number one priority is to build a better team - we will fill the holes in our squad during the [winter] break," new Besiktas president Hasan Arat told the AFP news agency.

Bailly spent seven seasons at Old Trafford after joining from Villarreal for £30m in 2016 but a combination of injury and form issues restricted him to just 113 appearances.

Like Bailly, Cameroon captain and striker Aboubakar, 31, and his international team-mate Onana, 23, only joined Besiktas this year. French right-back Rosier, 27, and Algeria winger Ghezzal, 31, have been with the club since 2020.