London Irish have been suspended from the Premiership after missing a deadline to pay players and staff.
The Brentford-based club, which is around £30m in debt, was given until Tuesday to complete a takeover or risk being suspended.
Irish, who finished fifth in the table in the 2022-23 campaign, will not be allowed to play in any league next season.
An American consortium have been trying to buy the club from current owner Mick Crossan, but the Rugby Football Union said the takeover had not materialised.
It means the third demise of a Premiership club, with Worcester Warriors and Wasps having suffered the same fate.
RFU chief executive Bill Sweeney said: “This is desperately sad news for everyone who is part of the London Irish community as well as all the players, fans, staff and volunteers for whom this club means so much.”
The club was recently served with a winding-up petition by HM Revenue & Customs over an unpaid tax bill.
Petitions were filed at the High Court on Friday against London Irish Holdings Limited and London Irish Rugby Football Ground Limited.
Sweeney insisted the RFU had worked with the club, Premiership Rugby and the Rugby Players’ Association to “do the utmost to secure the long-term viability of the club”.
But he added: “To achieve this, it was imperative that transparent evidence of funding be presented to us.
“This would have been either by the proposed buyers undertaking to provide all required working capital to meet the club’s obligations for at least the 2023-24 season; or the club providing evidence that it would continue to fund its operations throughout the 2023-24 season.
“Despite requesting this evidence over the last six months and receiving assurances on multiple occasions that we would receive proof of ownership and funds; it has not materialised.”