Sources inside the United camp are playing down the significance of such a move but there is little doubt that it would increase the focus on chairman Sir Roy Gardner and chief executive David Gill.

Magnier and McManus’ legal team are currently looking at United’s official response to the 99 corporate governance questions they posed last month that highlighted what they believed to be flaws in the club’s financial structures, particularly the amount of money paid out to agents.

Gardner and Gill are nervously awaiting their major shareholders’ next course of action, knowing if they do not find the response satisfactory, they could force an emergency general meeting, demand a place on the board or report their concerns to the Financial Services Authority.

If the share purchase does go through, it would also take them to within less than two percentages points of the 30% threshold for making an outright bid for the club.

United do not believe such a move is imminent although given the secrecy surrounding the motives behind Magnier and McManus’ increasing shareholding in the club, it cannot be ruled out.

The latest development will do nothing to appease angry United supporters, who have seen what had been a personal dispute between Magnier and manager Alex Ferguson over the stud rights to record-breaking stallion Rock of Gibraltar escalate into a row that threatens the fabric of the club.

Besides from singing anti-Magnier songs at recent United games, fans also staged a demonstration at Hereford racecourse last Friday where one of McManus’ horses was due to run.

Now it has emerged the "United 4 Action" group has asked Cheltenham racecourse executives if they can hold a "peaceful but vocal" protest on Gold Cup day on March 18.

“We don’t want to cause any disruption but we want to get the message across to John Magnier and JP McManus that we want them to sell their shares in Manchester United and give the club back to the fans,” said United 4 Action founder Sean Murphy.

“We’ve been in touch with the authorities at Cheltenham asking for permission to be able to hold a peaceful, vocal protest – at a place they designate.

“I’m still waiting to hear back from them but if the racecourse doesn’t give us permission we will revert to Plan B, which is to protest at a time and place at the track that has already been arranged.

“I’m not going to say where or when that will be – but it will cause huge embarrassment.”

That news will be greeted with alarm by Gill, who on Saturday urged supporters to stop their protests.

“While the board understands the concerns of the fans, it cannot possibly condone any disruptive or criminal activity and would urge all fans to refrain from such action as this will do damage to the reputation of the club,” said Gill.