Mike Ashley has written to Derby's administrators to confirm he remains interested in the takeover, an email seen by Sky Sports News has revealed.
Derby's future remains uncertain after preferred bidder Chris Kirchner failed to complete his deal for the club before Friday's 5pm deadline set by the administrators.
Quantuma announced on Thursday they were re-opening negotiations with other interested parties as a "contingency" - giving Kirchner less than 24 hours to prove he had sufficient funds.
Former Newcastle owner Ashley has contacted Derby's administrators, Quantuma, through his lawyers and communicated that he "remains willing and ready to transact".
Ashley, who has been interested in buying Derby since October after he sold Newcastle, has made offers in the sale process but not received any response from Quantuma for some time.
The letter sent to the lawyers of Quantuma on Ashley's behalf says he has been "disappointed by what [he] considers has been the failure of the joint administrators to engage constructively" during the process.
It adds that Ashley does not wish "to be treated as a contingency measure and would require some form of security" from the administrators before entering into further discussions over the sale of Derby.
Despite missing Friday's deadline, Quantuma have said preferred bidder Kirchner "continues to work" on providing the money required.
It is thought that if Kirchner's deal does fall through there is real danger the club - relegated from the Championship this season - could be liquidated.