Privately owned retail group Bestway, the owner of Costcutter, has built a 3.45% stake in Sainsbury's.
It described the move as an investment and not a step towards making a takeover offer for Britain's second largest supermarket group.
Bestway bills itself as the seventh largest family-owned business in the UK with turnover of about £4.5 billion.
It said today it intends to hold its shares and looks forward to supporting the executive management team.
It said it may look to make further market purchases of Sainsbury's shares from time to time, subject to availability and price.
"Bestway Group confirms that it is not considering an offer for Sainsbury's," it said.
Sainsbury's noted Bestway's announcement.
"We will engage with Bestway Group in line with our normal interactions with shareholders," it said.
The 3.45% stake makes Bestway Sainsbury's sixth largest investor, Refinitiv Eikon data showed.
Sainsbury's shares were up almost 6% in early trade at their highest since April and leading gainers on London's FTSE 100 index.
The stock closed at 239.4 pence yesterday, valuing the business at £5.6 billion.
Earlier this month, Sainsbury's reported better-than-expected Christmas trading.
Bestway said it started as a chain of convenience stores in 1963 and has grown to become a diversified multinational business with interests across the wholesale, pharmacy, real estate, cement and banking sectors.
It said it serves over 12 million customers and employs over 28,000 across the UK, Pakistan and the Middle East.
