Tampa Bay Buccaneers owner Malcolm Glazer has confirmed that he has increased his stake in Manchester United to more than 25 percent.

In a statement to the London Stock Exchange, Glazer’s company said it had purchased an additional 15,390,736 shares at $5.13 per share, bringing his stake in the club to 666,381,265 shares.

The club’s largest shareholders, Irish racehorse owners John Magnier and J.P. McManus, own 28.89 percent of the club through their company, Cubic Expression.

The Glazer family and the two Irishmen now own more than half the club. If either party reaches 30-percent ownership, stock market rules require a formal takeover bid.

Manchester United supporter groups have mounted a campaign to try and prevent Glazer securing a majority shareholding.