London Welsh face an RFU competitions hearing after being charged with fielding an ineligible player in "a number of" Premiership games.
The RFU has announced that the hearing will take place on March 5 in London.
The issue relates to the registration of scrum-half Tyson Keats.
The governing body also said that London Welsh's former rugby manager Mike Scott is the subject of a separate RFU disciplinary hearing relating to the registration of the same player.
Scott 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.
London Welsh, Premiership newcomers this season, are currently three points above bottom club Sale Sharks with six league games remaining.
Should the Keats matter go against them, they could be facing a considerable points deduction and probable fine.
It is understood that Keats was ineligible for nine Premiership games that he appeared in this season.
The news will be a hammer-blow to the club, who were promoted via last season's Championship play-offs.
In a statement, the RFU said: "London Welsh are to appear at an RFU competitions hearing charged with fielding an ineligible player in a number of Aviva Premiership matches this season.
"The case relating to the registration of scrum-half Tyson Keats will be heard on Tuesday, March 5, by a panel of Jeremy Summers (chairman), Premiership Rugby chief executive Mark McCafferty and Dr Julian Morris at the offices of Slater & Gordon, Chancery Lane, London.
"The club's former rugby manager Mike Scott is the subject of a separate RFU disciplinary hearing relating to the registration of the same player, and has been charged under RFU Rule 5.12 for 'conduct prejudicial to the interests of the Union or the Game'.
"That case will be heard at a later date."
London Welsh said that they brought the matter to the RFU's attention after conducting an internal investigation earlier this month.
The club also said they wanted to stress than no fault in the matter resides with Keats.
London Welsh 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 next week.
"Due to the sensitive nature and the impending hearing, the club is unable to make any further comment at this time."
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