Reuters: Stade Rennais issued a statement on Thursday criticising the behaviour of Nemanja Matic after the Serbian midfielder missed training without permission.
Matic, 35, joined the Ligue 1 club in August last year from AS Roma, having spent one season at the Serie A club, and previously played with Manchester United and Chelsea. He has made 19 appearances for the French club this season.
"Stade Rennais F.C. midfielder Nemanja Matic has failed to turn up for the most recent training sessions with the professional team," the club statement said.
"This behaviour is totally incomprehensible from an experienced player under contract until 2025."
French media have reported that Matic left the city in a bid to force a move away from the club.
"Always concerned by the wellbeing of its players, the club would like to point out that all the arrangements necessary for the successful integration of Nemanja Matic and his entourage have been carried out in complete transparency," the club added.
"SRFC is now awaiting the player's explanations and is determined to take all necessary measures to protect its interests."
Later on Thursday, Matic explained he was absent because he was trying to find a suitable school for his children.
According to some media reports, the club's executives had promised that the midfielder's children would be enrolled in an international school but there is no such school in the French city.
"Unfortunately, due to my mistake, I did not manage to adapt my private things to my professional one. I could not enroll the children in the international school," Matic said on Instagram. .
"That's why I was away last three days to try to solve this big problem for me and my family and tomorrow (Friday) I'm going back to Rennes where I will decide next steps together with the club."
Rennes are 10th in the Ligue 1 standings and host Nice on Saturday.