Chris Kirchner has been given until Friday afternoon to provide satisfactory evidence he is in a position to complete his takeover of Derby.
Administrators for the Sky Bet League One club have also opted to engage with other interested parties as a contingency measure.
American businessman Kirchner and the joint administrators exchanged contracts on May 16 and, while the purchase agreement remains in place, a deal is yet to be finalised.
The English Football League said it is “incredibly disappointed” by the latest update and called for a resolution “as a matter of urgency”.
“At the time (of exchanging contracts) there were a number of outstanding issues, which have now been resolved,” read a statement from the joint administrators of Derby.
“However, certain logistical issues mean that completion has still not taken place. Accordingly, the joint administrators have taken the decision to engage with other interested parties as a contingency measure.
“The sale and purchase agreement with Mr Kirchner currently remains in place and Mr Kirchner has been given until 5pm on 10 June 2022 to provide satisfactory evidence to the administrators that he is in a position to complete, subject to EFL approval.”
Derby were relegated from the Championship last season after being deducted a total of 21 points having fallen into administration.
Kirchner’s ownership of the Rams has already been given conditional approval by the EFL.
While administrators Quantuma said there remains a “real willingness amongst all parties” to conclude negotiations, the league expressed frustration at the protracted nature of proceedings.
“The EFL is incredibly disappointed with this evening’s announcement by Derby County’s administrators that Chris Kirchner has failed to complete the purchase of the club,” read an EFL statement.
“It is imperative that this issue is resolved as a matter of urgency.
“The league will continue to engage with Quantuma as they now hold discussions with third parties and will support as appropriate the club as it seeks to exit administration.”