Following Cesena’s relegation to Serie B at the end of last season, the attacker moved to the Ligue 1 team at the start of the season.
Since his arrival at the club, the former Chelsea man has netted twice in 11 appearances, but his old boss did not feel this was enough following to justify the player's reputation.
"When Mutu arrived he was not physically in the game and he did not bring what we expected of him. I may have put him on the field a little too quickly. When I recruited Mutu, I thought he would bring more to the team," he told RMC Sport.
"I cannot accept it all. His level of attitude and behaviour was largely insufficient. His state of mind was a bit complicated."
The 33-year-old has won 75 caps for Romania, and represented the likes of Chelsea, Juventus and Fiorentina.