London Welsh's Aviva Premiership fate could be decided today when the club appear in front of a Rugby Football Union competitions hearing.
The Exiles are charged with fielding an ineligible player - scrum-half Tyson Keats - in "a number" of Premiership games this season.
Press Association Sport understands 31-year-old Keats, who joined the club from now-defunct Italian side Aironi, was ineligible for nine of the 14 top-flight games he has featured in this season.
Welsh, who had to go through an RFU appeals procedure last summer just to secure their Premiership place, are currently locked in a relegation battle with Sale Sharks and London Irish with five games of the season remaining.
Sale occupy bottom spot at the moment, with London Welsh three points clear of them and Irish a further two ahead in 10th place.
Should the hearing go against the Exiles, they face the possibility of a hefty points deduction - which could be enough to relegate them - as well as a probable fine.
London Welsh's former rugby manager Mike Scott is also the subject of a separate RFU disciplinary hearing relating to Keats' registration.
He has been charged under RFU Rule 5.12 for "conduct prejudicial to the interests of the Union or the Game". Scott's case will be heard at a later date.
The Exiles may hope for some leniency after they themselves brought the matter to the RFU's attention having conducted an internal investigation in February.
In a statement at the time, chief executive Tony Copsey said: "This is obviously a serious matter which the club has not only brought to the attention of the RFU, but is also working closely with the RFU to provide full co-operation while the case is being prepared and ultimately heard.
"Due to the sensitive nature and the impending hearing, the club is unable to make any further comment at this time."
The panel for the hearing will be chaired by Jeremy Summers, who will be joined by Premiership Rugby chief executive Mark McCafferty and Dr Julian Morris.