Carrefour has started searching for a successor to its chairman and chief executive Georges Plassat, whose mandate at the helm of Europe's largest retailer expires in May 2018, sources said on Tuesday.

Since taking over as CEO in 2012 Plassat has led a recovery at Carrefour, focussing on price cuts and accelerating expansion into convenience stores and renovating stores to boost growth.

Plassat, 67, won a second three-year mandate in June 2015. Earlier that same year he underwent surgery and named Chief Financial Officer Pierre-Jean Sivignon and Secretary General Jerome Bedier as deputy CEOs to assist him.

At the May 2016 AGM Plassat said he was going to prepare his succession.

"In October Georges Plassat asked the board to start the process," a source close to Carrefour told Reuters.

Executive search firm Egon Zehnder cabinet has been mandated to select potential candidates.

"No specific scenario has been retained at this stage, the process has simply been launched," the same source added. The issue of whether the group will eventually split the CEO and chairman roles has also yet to be decided.

Plassat is said to favour keeping the same governance structure and recruiting a successor within the French retailer's ranks.

The group's top shareholders, which notably include two famous retail families, however want to keep all options open for the search.

"It is normal that the big shareholders also look elsewhere. The process is taking place in good terms with the CEO, even if the views may diverge", said one source close to the big shareholders.

The Moulin family, owner of French department store Galeries Lafayette, is Carrefour's top shareholder with a 11.51 percent stake, followed by Groupe Arnault with a 8.95 percent stake.

The family of Brazilian retail tycoon Abilio Diniz, has a 8.05 percent stake and private equity firm Colony Capital 5.23 percent.

Another source close to the matter denied recent media reports that Galeries Lafayette Chairman Philippe Houze could be eying Carrefour's chairmanship.

"Philippe Houze absolutely does not target the board chairmanship. It's totally false," the source said.