Marseille boss Didier Deschamps has called for Stephane Mbia to curb his erratic ways and rediscover his true form.
The Cameroon international, 24, was one of the French club's best performers in their run to the Ligue 1 title last season but he has failed to build on that so far this term.
A series of high-profile errors has earned criticism of the versatile defender, who began the season sidelined through injury, and Deschamps has addressed the issue.
"I believe he is capable to do more, much more, and Stephane knows it," Deschamps told L'Equipe.
"It is a lot of things, he has the right abilities. Then, it is about steadiness. He had a difficult start to the season with some problems that disturbed his concentration.
"The risks he takes does not make me laugh. And if I would be on the pitch with him, it would not make me laugh either.
"To me, simplicity means efficiency," he added.
Mbia, who reportedly attracted interest from Real Madrid and Manchester United in the summer, joined Marseille from current Ligue 1 leaders Rennes for an undisclosed fee believed to be in the region of £10million in July 2009.