SAO PAULO (Reuters) - Brazilian investor Nelson Tanure has initiated preliminary discussions with French retailer Casino,about buying at least part of its shares in supermarket operator GPA,, according to a source familiar with the matter, potentially adding to a stake amassed by funds allied to Tanure in recent days.

Tanure, who generally invests in distressed companies, recently agreed to acquire the Brazilian arm of Spanish supermarket chain Dia, which has been through restructuring proceedings.

Tanure declined to comment, and Casino, which owns a 22.5% stake in GPA, did not immediately respond to requests for comments.

The source said talks are still "superficial" and involve a demonstration of "intentions".

Earlier Monday, GPA announced in a regulatory filing that funds managed by Reag Trust Administradora de Recursos acquired a 9.56% stake in GPA, including some operations involving derivatives. These deals were funded by Tanure, the same source indicated. The news sent shares of GPA up 14% in Monday's trading.

Looking ahead, Tanure is considering proposing a merger between Dia and GPA, contingent on regulatory approval, the source added. Valor Economico newspaper first reported Tanure's interest in merging the two companies.

After years of debt-fueled acquisitions, Casino has restructured its operations to avoid bankruptcy. In March, GPA completed a primary offering of new shares, during which Casino relinquished its controlling stake in the firm as part of its strategic withdrawal from Latin America.