Professional football clubs and their players - past and present - may face bankruptcy over the non-payment of taxes, which could total up to £100m.
A legal test case, scheduled for the Supreme Court in March, will see Scottish Premiership club Rangers and HM Revenue and Customs lock horns on March 15.
Victory for HMRC is expected to prompt a wave of aggressive tax demands to professional football clubs across the UK, while rugby union and rugby league clubs may also be affected.
The case centres on the use of Employee Benefit Trusts (EBTs), which the Revenue suggests have allowed clubs and players to avoid paying tax on wages, dating as far back as 1999.
If HMRC win the case they will demand income tax, PAYE and National Insurance payments, plus interest - and demands are expected to reach close to £100m.
There is no upper limit on the sums sought by HMRC; clubs could be hit with Accelerated Payment Notices (APNs) immediately and would have 90 days to either contest the demands or pay up.
The scale of the crisis is difficult to judge as the use of EBTs is often not made public.
Andy Wood, a tax expert and director at Enterprise Tax Consultants has told Sky Sports News HQ that EBTs were widely used, with some players receiving as much as 50 per cent of their wages via the schemes.
He said: "EBTs were a staple diet in professional football for more than a decade; in particular between 1999 and 2010.
"The vast majority of Premier League clubs, plus more than half of clubs in the Championship, were using EBTs to help pay their players. Most of those loans are still outstanding."
Some of football's leading clubs have already paid HMRC officials in order to avoid being hit with large income tax demands, and several clubs are understood to have reached private settlements with HMRC in recent months due to concerns about its investigations into EBTs.
Wood has been involved in helping one club reach a six-figure agreement with HMRC in relation to the affairs of one senior official and was aware of "five or six" other such deals being struck.
Other Premier League clubs are understood to have recently received hefty tax demands after disclosing their own use of EBTs between 1999 and the present day.
If HMRC lose the Supreme Court battle in March, however, it is understood the clubs will escape further investigation, with attentions turning instead to the players themselves.
This is likely to cause exaggerated problems for retired players who benefited from EBTs but are no longer able to generate funds needed to pay.
Wood added that HMRC's pursuit of what it regarded as the abuse of EBTs could see some of football's biggest names facing bankruptcy as a result of big tax demands.
He said: "Although most of the immediate financial burden rests with clubs which have put these schemes in place, players who have taken loans from the trusts may not be spared, as an imminent change in the law would require them to pay tax on monies not repaid by 2019.
"Being asked to stump up large sums may come as a shock for players, especially those in retirement who do not have the earning capacity which they once might have had. Some might even be forced into bankruptcy if they can't meet those demands.
"I have been in discussions with a number of football, rugby union and rugby league clubs regarding their remuneration schemes. They are now all too aware about how the process entails keeping both star players and the taxman happy."
An HMRC spokesperson has told Sky Sports News HQ: "HMRC does not do deals and we don't settle for less tax from EBTs than we could get from going to court.
"HMRC is committed to delivering a level playing field for all taxpayers, ensuring those who have used these schemes don't derive any long term advantage over those who play by the rules."