The Scottish Premier League have offered assurances that their investigation into alleged undisclosed payments by Rangers is progressing.
The SPL released a statement hours before a BBC1 Scotland documentary on the finances of Rangers, which includes examination of the Employee Benefit Trusts the club used in an attempt to reduce their tax bill.
An SPL spokesperson said: "The investigation into the EBT payments made by Rangers FC is being actively pursued on behalf of the SPL.
"All relevant documents, materials and information have been sought from Rangers FC and we look forward to receiving full co-operation from the club and its administrators in providing everything that it and they have access to and which is required for the investigation to be completed."
The SPL launched their investigation into the matter on March 5, with the probe covering the period stretching back to the competition's inception in 1998.
SPL rules prohibit payments to players that are not made "in accordance with a form of contract approved by the SPL".
The league instructed their lawyers, Glasgow firm Harper Macleod, to investigate the matter.
The BBC publicity around the programme, Rangers - The Men Who Sold the Jerseys, says it is based on "dozens of secret emails, letters and documents which uncover the truth behind the tax scheme which threatens the club's very existence, and reveals what went on behind the scenes in the run-up to Craig Whyte's infamous takeover".
Investigative reporter Mark Daly, who uncovered Whyte's disqualification as a director in a programme aired in October, revealed more details of his programme on Twitter.
He said: "Biggest EBT beneficiaries named, did Whyte really "dupe" Sir David (Murray) and questions over the administrators."
Daly also promised revelations over the issue of dual contracts, the existence of which was alleged by former director Hugh Adam but denied by former owner Murray.
The use of EBT payments was the subject of a tax tribunal in January with the outcome still to be announced, but Rangers could be liable for a bill of up to £75million.
The club previously admitted liability to the tax authorities for a £2.8million scheme which benefited Tore Andre Flo and Ronald de Boer between 1999 and 2003, although they did not pay before going into administration in February over an unpaid tax bill of £13million.Rangers' administrators, Duff and Phelps, later responded to the SPL statement.
Paul Clark, joint administrator, said: "The use of EBTs at Rangers goes back many years and was a matter of public record in the annual accounts.
"Our primary focus has been ensuring the survival of Rangers Football Club and attracting a new buyer for the business as well as investigating the financial situation at the club since the takeover in May 2011.
"We and the club will continue to give every assistance to the football authorities on issues affecting the club.
"It should, however, be noted that the First Tier Tax tribunal has yet to publish its findings in relation to the use of EBTs."