Balotelli, 28, revived his career at the modest French side after underwhelming stints with Liverpool and AC Milan - where off the field issues collided with his promising career.
A record of 43 goals in 66 games over the past two season saw his stock dramatically rise within Europe, but his recent behaviour has once again thrown his future into doubt.
The Italy international did not attend the start of preseason training last month, arriving at the club two weeks later after talks over a proposed move to Marseille stalled due to contractual disputes.
"It's going to be very complicated, very difficult, as the player wants to leave," he told Canal Plus.
"What's important, for me and for the club, is to keep players who want to help the club improve -- and from the moment Mario has decided he wants to leave, the club has to do what's necessary to let him leave."