Sainsbury's became a takeover target for the second time this year after revealing an approach from a fund backed by the Qatar royal family.
The Delta Two investment fund already owns 25% of the supermarket chain after buying shares in recent weeks.
A private equity consortium pulled a £10.1 billion takeover attempt in April after failing to win the support of the founding Sainsbury family.
A brief statement from Sainsbury's confirmed it had received a preliminary approach from Delta Two, which it said "may or may not lead to an offer being made for Sainsbury's".
Delta Two has so far been tight-lipped about its interest in Sainsbury's. But analysts have focused on the retailer's £8.6 billion property estate, which could be separated from the main business in order to unlock value.
This is something that the Sainsbury's board has ruled out, as it would not want to burden itself with significant additional rental and interest costs.
Speculation over a possible approach from Delta Two grew last month following its purchase of a further 7% stake in the blue-chip company for £732 million.
The investment fund paid 13p a share higher than the 582p-a-share reportedly offered by a CVC-led private equity consortium in April.
It was also reported last month that Delta had held informal talks with investment banks over co-financing a bid for the retailing giant.
Delta Two confirmed it was in preliminary discussions with the Sainsbury's board, but said no decision had been made regarding a possible offer.
