Bill Miller was given assurances from the Scottish Premier League and the Scottish Football Association before he took a step closer to taking control of Rangers, according to the club's administrators.
The American businessman, who was vying for control with the Blue Knights consortium led by former Ibrox director Paul Murray and backed by Sale Sharks owner Brian Kennedy, was named preferred bidder for Rangers on Thursday.
Miller's plan is to create what he described as an "incubator" company while Duff and Phelps bid to take the club out of administration through a Creditors Voluntary Arrangement (CVA), and he also immediately promised to end the culture of over-spending at the club.
Miller had previously sought assurances from the football authorities that his 'newco' club would not be subjected to sanctions next season.
Completing his transaction before the season ends on May 13 would ensure his request to acquire Rangers' share in the competition is subject to the discretion of the SPL board. SPL clubs will vote on financial fair play proposals, which include financial and points penalties against newco clubs, on Monday but the rules would not take effect until May 14 anyway.
Last Saturday around 7,000 Rangers fans marched to Hampden in protest at the penalties imposed on the club by the Scottish Football Association, which include a one-year transfer ban and a £160,000 fine relating to charges of rule breaches, although the club are in the process of appealing the verdict.
Rangers are also being investigated by the SPL over alleged undisclosed payments to players since 1998.
Duff and Phelps' David Whitehouse told Press Association Sport: "Bill Miller's bid has been conditional upon him reaching terms with the SPL and SFA in relation to on-going sanctions. Until today his bid was conditional, now it is unconditional, so I can guess you can assume from that that he has the level of comfort that he needs to proceed.
"Effectively what we have created is a scenario where Bill Miller will acquire the business and assets of the football club in a new entity, so that club and company can be taken forward free from the existing problems which were associated with the old club, while the process of administration continues to clean up the old club."
Miller said: "Under my stewardship, Rangers will be managed with fiscal discipline such that the club not only conforms to UEFA financial fair play regulations but also such that Rangers will never have to suffer this kind of anguish again."