An investigation into the matter – which centres around Sir David Murray's ownership of the Ibrox club – is continuing following allegations made by former director Hugh Adam.
This, of course, would mean a breach of the rules and Doncaster says any potential penalties could follow the football club over to any newco.
He said: "It will take some time and ultimately it's being done by our lawyers. They will bring the case forward to us and the SPL board when they can do so.
"How long will it take? How long has the HMRC case taken? These things take as long as they take. These are complicated matters, far more complicated than people might think."
With regard to possible sanctions, he said: "The issue will be; have any of our rules been breached? If there is a prima facie case that they have then we will act accordingly.
"The rules are there and all clubs are treated equally under the current rules.
"The investigation is going on in accordance with the rules set down at various stages of the SPL's history.
"There is only one rule within our whole set of rules where the breach has a pre-determined sanction. "If you go into administration the sanction is a 10-point sporting penalty, perhaps to be increased.
"All the rest of the other rule breaches have 18 potential sanctions, unlimited in scope.
"Whoever makes the decision on any disciplinary matter, be it the board or an independent commission, there is no set sanction in place.
"There is no point in trying to project where a club might be.
"You deal with the process and you get out. The rules are what they are; we apply the rules and you get out."
When asked if players would be ineligible if contracts were found to be in breach of the rules, Doncaster replied: "It's more complicated than that.
"That's why it's important that we give the investigation room to come back, present the board with the rules and what they have found and a recommendation.
"You would expect the football club in question to take with it the responsibility for anything which emerged from that investigation."