Around 30 lawyers have filed a court complaint against Darmain accusing him of tacitly supporting Sarkozy.
The justice minister visited the 70-year-old in the Paris prison La Santé on Wednesday and discussed security arrangements there, despite warnings from prosecutors that such a visit could jeopardize the view of the judiciary as independent.
"I feel very sad about (what happened) to President Sarkozy. I was his colleague and I cannot be insensitive to another man's plight," Darmain recently told France Inter television.
The ex-president is reported to have been one of Darmain's political mentors.
Right-wing politician Nicolas Sarkozy, President of France from 2007 to 2012, was convicted about a month ago of "criminal conspiracy" for financing his 2007 presidential campaign with financial support from Muammar Gaddafi's Libya. He has appealed the five-year prison sentence, but he began his prison sentence last week, awaiting a new trial.
