The 61-year-old is thought to have been in the house when the attack occurred, with paint also being sprayed on an Audi and over parts of his house.

Watkins was unavailable for comment this morning but it is thought the attack is part of a concerted campaign to prevent American business tycoon Malcolm Glazer taking control of the Red Devils.

Watkins is the largest individual shareholder on the United board, owning a 1.9% stake, valued at approximately £13m (€18.9m).

He is a long-standing member of the Old Trafford board, is also the club’s legal adviser and is widely respected in the football world having worked extensively with UEFA and FIFA drafting the new transfer regulations. He was also the man who publicly announced United’s intention to fight Rio Ferdinand’s eight-month ban for a missed drugs test.

However, he attracted the ire of United fans in April when a million shares he put up for sale ended up in Glazer’s hands.

Even though Watkins had no prior knowledge of who the shares would be sold to, fans have accused the solicitor of selling United’s heritage and aiding Glazer’s attempts to purchase the club.

Glazer, who is also owner of the Tampa Bay Buccaneers NFL franchise, is widely believed to be behind the "preliminary approach" to buy the club, which was confirmed to the Stock Exchange yesterday morning.

United fans’ groups are opposed to any takeover. They have vowed to fight a "dirty war" to keep their club out of Glazer’s clutches and it appears Watkins could be the first victim.

Their previous tactics included staging a racecourse protest at Hereford earlier this year in response to the intervention of major shareholders John Magnier and JP McManus, who will be pivotal to Glazer’s chances of taking control.

The Irish racing duo knew nothing of yesterday’s announcement but with their own stake standing at 29.3% agreement is essential for Glazer to stand any chance of succeeding in his aim.

United are currently waiting for clarification of the initial proposals, which saw the club placed into an ‘Offer Period’ for the second time this year.

At some point, Glazer will either be forced to announce he has made a bid or inform United he has not, which would preclude him from making another attempt to seize control for a further six months.