Shares in Tesco climbed as much as 2% on Friday after it emerged that a firm owned by the world's second-richest man had built up a stake in the chain.
Warren Buffett's Berkshire Hathaway investment company has bought 2.9% of the supermarket giant's shares.
Details were disclosed by Mr Buffett in a letter to his stakeholders.
Tesco shares have climbed about 12% in the past three months. They fell back to a 1% gain in intra-day trading by 1200 GMT on Friday.
Mr Buffett, who amassed his fortune from investments, is worth an estimated $44bn, according to Forbes magazine.
However, he said last year he was going to donate about $37bn (£20bn) to Bill Gates' charitable foundation.