New Zealand Centre for Public Law associate director Dean Knight, of Victoria University, said the director-general did not appear to have the power to impose a decision on the boards.
The director-general became involved in the impasse over South Island neurosurgery services in May when the boards asked him to appoint an arbitrator empowered to ensure the matter was resolved urgently.
The terms of reference for the expert panel he appointed to advise him on the dispute stated his decision will be final.
Doubts raised about the legality of this have prompted repeated Otago Daily Times questions, to both Mr Ryall's office and the Ministry of Health, which remain unanswered.
Mr Knight said, under the New Zealand Public Health and Disability Act, the boards could delegate powers, but such delegation would have to be approved by the minister.
The boards' collective decision-making framework document under which the dispute was referred to the director-general did not indicate that such a delegation had been sought, Mr Knight said.
It referred to the director-general as a "default mediator" rather than an arbitrator.
The framework document correctly noted, in its second paragraph, that boards were autonomous entities and could not be forced into making decisions they did not agree with by anyone other than "a shareholding minister".
Mr Knight said it appeared to him, after viewing the framework document, the letter referring the dispute to the director-general, and the expert panel's terms of reference that "legally, the recommendation of the director-general would seem to be irrelevant".
Unless the boards agreed to abide by whatever he decided, they could not be forced to comply.
This would not necessarily pose problems if the director-general's proposal was accepted by all of the boards and their communities.
However, if , for example, the Southern board accepted the recommendation and people within its district did not agree with it, they could argue that the board was effectively letting the director-general make a decision which he was not allowed to make.
It was likely the parties were hoping the stalemate would be broken by reaching some sort of consensus, he said.
Southern chief executive Brian Rousseau, in response to a series of questions from the ODT, makes it clear that when the dispute went to the director-general, he did not consider the boards were giving him the role of decision-maker.
Instead, Mr Rousseau expected he would provide "non-binding arbitration where the director-general states a position he wishes to be adopted".
This would involve independent evaluation of the issues and an independent conclusion.
As he saw it, the South Island chief executives could either agree with the position taken by the director-general and recommend accordingly to their boards, or they could agree with the position "leaving it up to the director-general to activate mechanisms so as to direct the DHBs to adopt his recommendation, if he so wished".
Mr Rousseau advised that the Southern board, or the previous Otago and Southland boards, had not passed any resolution giving the director-general the power to direct them on this issue.
The ODT posed the same questions to lead chief executive for the South Island boards shared services planning, Chris Fleming (South Canterbury), who declined to comment, saying he would not be involved with any debate while the panel was carrying out its work.
Acting Director-general Andrew Bridgman has also not answered questions about his power and how it was bestowed.
In a statement this week, he said he was asked to make a decision by the South Island boards, referring to their decision-making framework as "a work in progress" which had not been tested before.
He said he was taking legal advice throughout the process to ensure it was fair and sound.
Further questions from the ODT and concern about the inadequacy of the ministry response have been ignored.
