Schultz, 50, who is joining Middle Eastern retail group Al- Futtaim, will be replaced by Franprix boss Jean-Paul Mochet.

Mochet, 54, a Casino group veteran, would continue as president of Franprix when he takes up his new position at Monoprix on July 15, Casino said in a statement.

The departure of Schultz, who joined Monoprix in 2016, comes at a tough time for Casino and its boss and majority shareholder Jean-Charles Naouri.

Casino shares were down 2.7% by 1134 GMT, bringing losses so far this year to 20%.

"Regis Schultz was known to be a visionary and to be one of M. Naouri’s potential successors," Bryan Garnier analysts said.

"His departure will raise some questions and concerns as we can wonder if other top managers will also leave the group while Rallye is about to enter into a tough negotiation period with its creditors," the analysts wrote in a note.

Casino's parent companies including Rallye were placed under protection from creditors last month in a bid to save the indebted French group from collapse.

Under Schultz, who previously headed electronics retailer Darty and worked for Kingfisher and Castorama, Monoprix said last year it would sell groceries via Amazon, the first French retailer to take such a step.

Mochet and Schultz have been seen as potential successors to 70-year-old Naouri, the chairman and CEO of Casino.

"There is no connection to make between these moves and Mr Naouri's succession, which is not on the agenda," a group spokeswoman said.

Mochet, who joined Casino in 2000, has been head of Franprix since 2008. He has been a member of Casino's Executive Committee since September 2013.

Monoprix is one of France's best-known store chains, with a network of nearly 800 upmarket stores in more than 250 cities and is a key contributor to Casino group's profit.

(Reporting by Dominique Vidalon; Additional reporting by Pascale Denis in Paris; Editing by Sudip Kar-Gupta and Edmund Blair)

By Dominique Vidalon