Rumours of an approach priced at about 500p per share spread through the stock market, which pushed shares up to 344p each, valuing the business at £6 billion.
One trader told The Times that there was speculation that the Qatari Investment Authority (QIA) was working on a bid with property tycoon Robert Tchenguiz and an unnamed investor. The QIA scrapped their £10 billion bid for Sainsbury's last year because of the credit crunch.
The QIA has a 27% stake in Sainsbury's, while Tchenguiz, who backed the original offer, holds a 10%.
A Sainsbury's spokeswoman said: "We can't comment on market rumour and speculation."