The US National Football League (NFL) has asked Tampa Bay Buccaneers owner Malcolm Glazer to explain Manchester United's links to a Las Vegas casino.
The NFL has problems with just one part of Mr Glazer's United takeover
A planned joint venture between the UK football club and the Las Vegas Sands could fall foul of NFL rules.
The NFL also ruled that Mr Glazer's control of United does not violate the League's rules on cross-ownership.
The League added it had no problem with the debt Mr Glazer has incurred as he garnered a controlling stake in United.
The news came during a meeting of NFL team owners, the first such meeting since Mr Glazer took a controlling share in the club - a move that has cost £790m, leading to fears he may use the Buccaneers as collateral for his debts.
The tycoon now owns around 76.2% of Manchester United and has made an offer of 300p a share to remaining investors.
He hopes to secure 90% of the shares he does not yet own, so that the remaining shareholders can be legally compelled to sell.
Whether or not he gains those remaining shares, Mr Glazer seems certain to delist the club by 30 June at the latest - ending 14 years of United's presence on the stock exchange.
United fans had hoped that NFL rules on cross ownership - owners owning other teams in other sports - would put paid to Mr Glazer's takeover.
But NFL spokesman Greg Aiello told the Associated Press news agency that Mr Glazer's investment had not broken any league rules.
United fans also tried to obstruct Mr Glazer's plans by setting out the club's links to gambling in a letter to the American Football ruling body.
According to AP, the letter written by JD Deitch said United has bookmaking stalls at its Old Trafford ground and has links to a gambling website from the club's official site.
The letter also outlined United's plans for a so-called "supercasino" as part of a proposal to regenerate the Salford Quays area of Manchester.
The NFL is known to be wary about gambling links and so has asked Mr Glazer for more information about the casino plans.
"The only potential issue concerns that reported Man United joint venture with the Las Vegas casino, what that means, and does it have any implications regarding our policies," Mr Aiello said.
However, no deadline has been set for Mr Glazer to offer his explanation by, Mr Aiello added.