Duff & Phelps would not confirm the organisation's identity yesterday, amid speculation a Middle Eastern consortium would be interested in buying the club.
Those still appearing to have an interest in a takeover deal include New York-based Fortress, an investment bank with assets of £27 billion.
Glasgow-based businessman Shazad Bakhsh had been expected to make a formal bid centred on Singapore by last Friday's initial deadline.
The Blue Knights consortium, Sale Sharks owner Brian Kennedy and Chicago-based Prometheus Capital Partners have all submitted conditional offers and the administrators are due to hold talks this week before asking a preferred bidder to reach agreement with creditors.
Meanwhile, the Court of Session yesterday heard Duff & Phelps claim one of the Rangers bidders has warned it will not pursue its interest in the Ibrox club if the Ticketus season ticket deal is in force.
They are seeking a resolution over the status of the Ticketus
contract, which involved the sale of the rights to four years of season tickets for more than £20 million to finance Craig Whyte's takeover at Ibrox.
While Whyte bought an 85% stake in Rangers for £1, £18m of the money raised was used to pay off the club's debt with Lloyds Banking Group.
The administrators want to break the deal so the tickets are invalidated and Ticketus becomes an unsecured creditor alongside Her Majesty's Revenue and Customs (HMRC).
The club's administrators are seeking guidance from the court on a potential move to breach the contract with Ticketus over season ticket rights for Rangers games.
Meanwhile, Sir David Murray last night told Sky News Scottish football would fall "into the wilderness" due to lack of finance if the club was forced out of the SPL. The former Rangers chairman said: "Anyone who says otherwise is kidding themselves. They're looking at it through green glasses or blue glasses."
He also criticised what he perceived as Rangers "coming under the spotlight" because HMRC wanted "a high-profile case" as an example to other debt-ridden clubs.