Otago board chairman Errol Millar said plans for the boards to hold another joint meeting on the issue had to be abandoned as a suitable time could not be arranged.
A planned meeting in Dunedin this month did not go ahead because some members had work commitments.
Mr Millar said it was proposed the Otago board would discuss the issue in the open part of its normal monthly meeting on October 1 and then move into a closed session to make a decision.
That decision would then be embargoed until after the Southland board met and made its decision a week later.
Asked whether it might be obvious from public discussion what the Otago decision would be, he said he did not know.
The purpose of the closed session decision and embargo was to avoid any influence on the Southland board which could unfairly impact on their decision.
He would be making it clear to members that they were not to disclose the decision to anyone and he would have to have trust and confidence in their integrity.
Chief executive Brian Rousseau advised there were several possible legal reasons under the Official Information Act the board could choose for making its decision in private.
They included maintaining the effective conduct of public affairs through protecting members from improper pressure or harassment, enabling the board to carry out commercial activities without prejudice or advantage, enabling the board to carry on negotiations without prejudice or disadvantage, and preventing the disclosure of official information for improper gain or advantage.
Mr Rousseau has yet to release the proposal the boards will consider, and Mr Millar said it was not expected this would be done earlier than the usual two days before the October meeting.
Mr Rousseau withdrew his proposal for a single PHO across both regions, replacing the existing nine, when board members indicated they would not reach agreement on this at the boards' joint meeting in Invercargill in August.
He has since said that it was no secret his preference was for a single PHO.
Mr Millar said there would not be a chance at the meeting for the existing PHOs to make submissions as there had been at the Invercargill meeting.
That meeting lasted more than four hours, with a considerable proportion of the presentations from PHOs and South Link Health.
They had been given a fair chance to be heard and it was time for the boards to debate the issue, Mr Millar said.
Mr Millar agreed it was possible the boards could arrive at different decisions.
While the matter was not put to the vote at the August meeting, indications were that there was more Otago support for a single PHO, while Southland members seemed likely to opt for a PHO for each region.
