Irish racehorse magnates J.P McManus and John Magnier have raised their holding in Manchester United to just over 24 percent from 23 percent previously, fuelling bid speculation.

Their investment vehicle Cubic Expression said in a statement on Monday that it now held 24.24 percent of Manchester United, one of the world's top sports teams.

Last month, U.S. sports entrepreneur Malcolm Glazer also raised his stake in the club to 14.31 percent.

Glazer owns Manchester United's MNU.L American Football equivalent, NFL Super Bowl champions the Tampa Bay Buccaneers, and recently met United executives to talk about the club's strategy.

However United executives said last week that they had not received any bid approaches from either stakebuilder.

Manchester United has been the subject of persistent takeover speculation since rival Chelsea was bought out by Russian billionaire Roman Abramovich in July.

Shares in Manchester United were up 1.2 percent at 269-3/4 pence on Monday at 1:20 p.m.