Rangers' administrators confirmed on Friday night that there had been "several" indicative bids for the club with at least one more on the way.
However, Duff and Phelps added that interested parties were looking for clarity on the club's financial affairs before lodging more detailed proposals.
Only Sale Sharks owner Brian Kennedy and the 'Blue Knights' consortium fronted by Paul Murray have confirmed they have submitted bids.
Reports claim Chicago-based Club 9 Sports has also lodged interest. The investment firm has previously failed with investment offers in Sheffield Wednesday and Tranmere.
Joint-administrator David Whitehouse said: "We believe the level of interest in purchasing the club from around the world reflects the pedigree and history of the club and the fact the financial position of the business is beginning to clear and will continue to do so over forthcoming weeks.
"However, it is evident from our preliminary assessment of the expressions of interest and indicative bids that prospective purchasers are looking for clarity on certain issues at the earliest possible opportunity prior to submitting more detailed formal bids.
"There are complex issues to be resolved and there is no doubt they are having a bearing on the bidding process. At this stage we have indicative and conditional bids only."
Administrators will now determine which bids offer the best deal to creditors and consider the attached conditions.