However, Sainsbury's has resportedly offered a more attractive bid than the Co-op and Nisa is now set to sign an an exclusivity deal with the Big 4 retailer that temporarily bans it from pursuing other bidders.
However, it is understood Sainsbury's offer, at around £2,500 a share, was favoured by Nisa's board.
United Kingdom retailer Sainsbury is said to be close to submitting a formal bid to acquire Nisa, a wholesaler and convenience store group that counts more than 2,500 independently-owned stores around the United Kingdom as members.
Each member has between one and 250 votes, and Nisa's board would need 50 per cent plus one vote in order to get approval for the sale. The deal not only brought Sainsbury's more retail sites and helped it extend its presence beyond the grocery/supermarket sector, but also gave it access to Argos's fast delivery capabilities.
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Nisa revealed last week that was looking to demutualise and seek a grocery buyer in light of Tesco's plans to merge with grocery wholesaler and convenience store operator Booker.
An investigation by the Competition and Markets Authority (CMA) would take place along similar lines to the one being carried out in respect to the Tesco-Booker tie up, they added. The move would come after FTSE 100 rival Tesco (LON:TSCO) inked a deal to acquire Booker Group earlier this year.
Sainsbury's, Nisa and the CMA declined to comment.