The Scottish Premier football League is investigating the way Rangers have paid their players since 1998, in the latest blow to the Glasgow club who are facing a battle for financial survival.
The move came after a former Rangers director alleged in a newspaper that players had in the past been given hidden contracts alongside their official ones.
Rangers already face a potential tax liability of more than a hundred million dollars relating to the use of Employee Benefit Trusts to pay high-earning players.
The club's administrators Duff and Phelps delayed an expected announcement of cuts to the squad after the players proposed wage cuts to try to prevent job losses.
Rangers have also held talks with cash-strapped English championship club Portsmouth about playing a friendly to try to raise funds for both teams.
Rangers look certain to surrender their Scottish league title to city rivals Celtic after being docked 10 points for going into administration over unpaid taxes.
Rangers now trail Celtic by 21 points after a home defeat by Hearts at the weekend.