London Irish have filed for administration after being suspended from the Premiership.
Irish, who will not be able to play in any league next season, were punished after missing a deadline to pay players and staff or complete a takeover.
Owner Mark Crossan and a US consortium have been unable to reach a deal.
Crossan, who bought the club in 2013, said administration had "always been the last resort" but was now the "safest path forward".
"We bitterly regret the difficulties it will present to each and every one of you," he said in a letter to staff.
"My focus is now on working with the appointed administrator and I hope that the club will come out of administration as quickly as possible."
Crossan said the decision to suspend the club from the Premiership was "bitterly disappointing".
"I understand the sadness felt by the thousands of our loyal supporters and the frustrations of our incredible coaches, medical staff, back-office team, and players," he said.
"This decision has ultimately ended any hope of an acquisition of the club and has regrettably forced us to file for administration."
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How did London Irish get here?
While Irish had a solid season on the pitch - finishing fifth and reaching the final of the Premiership Rugby Cup for the second successive season - there has been talk for some time of issues off the field.
The club are understood to have debts of about £30m, and Crossan had to step in to pay overdue wages in April, just minutes before players were preparing to submit breach-of-contract notices.
The club were initially given a deadline of 30 May to complete the takeover or risk being suspended from the Premiership next season, but the Rugby Football Union pushed that cut-off point back to 16:00 BST on Tuesday.
As well as either completing the takeover or proving they had funding to operate for next season, Irish had to ensure all staff and players were paid in full for May, after just 50% of the money had been forthcoming.
The club were last week served 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.
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