Rangers are facing court action from HM Revenue and Customs, it emerged on Tuesday.
It is believed the club are being investigated over offshore payments made to players. Rangers said they would defend themselves "robustly''.
A club spokesman said: "There is an ongoing query raised by HMRC, which is part of a pending court case. On the basis of expert tax advice provided to Rangers, the club is robustly defending the matters raised. It would, therefore, be inappropriate to comment further at this stage.''
The cash-strapped Ibrox club, who won the Scottish Premier League on Sunday, are £31 million in debt and have been put up for sale. Newspaper reports suggested that property developer Andrew Ellis is likely to launch a takeover.
An HMRC spokeswoman said: "HMRC cannot comment on the confidential tax affairs of individuals or businesses.''