Irish racehorse magnates JP McManus and John Magnier raised their stake in Manchester United FC to 25.49 per cent today from 24.24 per cent previously to prompt more bid speculation.
The pair's investment vehicle, Cubic Expression, said in a statement it had bought 3,256,944 shares in English soccer's reigning champions, to take its total holding to 66,543,837 Manchester United shares.
An investor who builds up a 30 per cent stake in a British company is required to make an offer to all other equity shareholders, according to Takeover Panel regulations.
Manchester United, one of the world's richest soccer clubs, has been the subject of persistent takeover speculation since rival Chelsea was bought out by Russian billionaire Roman Abramovich last July.
Manchester United's second biggest shareholder is US sports entrepreneur Malcolm Glazer who raised his stake in the club to 14.31 per cent in November.
Glazer owns last year's top American football club, the Tampa Bay Buccaneers, which will give up their NFL Super Bowl crown next week after failing to make this season's playoffs.
At noon today, United's shares were up 1.2 per cent at 256.5 pence, valuing the club at £684 million sterling. Earlier today, United confirmed it had agreed in principle to buy Fulham striker Louis Saha for an undisclosed fee.