Florida-based American football magnate Malcolm Glazer has increased his stake in Manchester United.
The Premiership club said on Friday that Mr Glazer held 8 million of the club's shares, about 3.17% of the total.
Under UK stock market rules, investors whose holdings in a firm rise above a 3% threshold are obliged to inform its management.
Mr Glazer, owner of the Tampa Bay Buccaneers American football team, has been linked with persistent speculation of an effort to take over Manchester United.
The club, owner of one of the most well-known global sporting brands, is thought to be in the sights of a number of potential buyers.
There were rumours earlier this year that Mr Glazer was weighing up a bid for the club, possibly in conjuction with three other Man Utd shareholders - Irish horseracing tycoons John Magnier and JP McManus, and Dutch television entrepreneur John de Mol.
More recent takeover speculation has centred on an unidentified Russian billionaire and a Middle Eastern businessman, also unnamed.
Rumours of a foreign buyout have gathered pace following the surprise takeover of Manchester United's premiership rivals Chelsea by Russian oil billionaire Roman Abramovich.
However, Manchester United would not come cheap, with an estimated price tag of about £600m ($960m).
Manchester United shares were down 2.5p at 193p in mid-morning trade on Friday.