THE Scottish Football Association has asked every club in the country to admit whether it made undisclosed payments to players at any point over the past 10 years.

The governing body wants clubs to admit if they paid any money to players outwith the contracts which are submitted to and registered by the SFA. The SFA wrote to its 93 member clubs on March 9 and gave them an April 6 deadline to confirm that they had complied with the rules.

Details of the letter emerged last night as Rangers faced renewed accusations from former director Hugh Adam that undisclosed payments were commonplace at the club before he left the board in 2002. Former owner Sir David Murray has denied those allegations but they are the subject of an investigation by the Scottish Premier League.

The allegations made by Adam last month, and repeated in a Channel 4 News investigation last night, concern undisclosed payments to numerous Rangers players via Employee Benefits Trusts. Rangers admit using EBTs between 2001 and 2010 – the amount of tax they paid on them is the disputed subject of the potentially crippling big tax case which could leave them liable for £49m – but Murray has insisted there were no "second contracts" or "side letters" which had to be registered with the governing bodies. Murray has referred to the scheme as "non-contractual and discretionary".

The letter asks clubs to notify the SFA of any potential breaches of rule 12.3, which states: "All payments, whether made by the club or otherwise, which are to be made to a player solely relating to his playing activities, must be fully recorded within the relevant written agreement with the player prior to submission to the Scottish FA and/or the recognised football body of which his club is in membership."

Stewart Regan, the SFA chief executive, said his organisation had been made aware there could be "a number of examples of non-compliance" with the rule.

Meanwhile the SFA may revise its "fit and proper person" criteria in the aftermath of Craig Whyte's controversial purchase of Rangers. A proposal being considered by Regan would put the onus on any outgoing owner, such as Murray, to do far more rigorous checks on the person to whom he was selling the club. After an independent inquiry under Lord William Nimmo Smith the SFA this month declared Whyte to be unfit because of his undisclosed previous disqualification as a company director.

Murray claimed he was "duped" by Whyte but Regan said the SFA would consider whether more could be done in similar circumstances in the future. He said the SFA would continue to rely on the clubs to be the primary source of investigation on new investors. "That said, I think there are a number of learnings and I think the same goes for football right across the globe," said Regan. "We are currently exploring the possibility of carrying out due diligence using the outgoing regime to make sure there's a full and rigorous set of research done before the transaction is allowed to go ahead."

Rangers' administrators, Duff & Phelps, have been made aware of a fifth party preparing a bid for the club, to join the Blue Knights, Brian Kennedy, Club 9 Sports and an overseas consortium.