Dr Tony Holohan is set to return as NPHET meets to consider if the country should reopen on October 22.
The easing of most restrictions on this date has been flagged for months, and until recent days had been expected to proceed as planned.
However on Wednesday government leaders began to raise the alarm after concerning Covid-19 trends emerged.
Public health experts including Deputy Chief Medical Officer Dr Ronan Glynn signalled that the pattern of the disease may be changing, and Taoiseach Micheal Martin now said he cannot guarantee that the October 22 reopening will proceed as planned.
It had been expected that the majority of Covid-19 restrictions would be permanently eased on this date.
But now a final decision will not be made by government until after NPHET meets to discuss the current situation.
And now it has emerged that Chief Medical Officer Dr Tony Holohan will return from annual leave to chair the key meeting on Monday.
NPHET will pass on its recommendation to government with a final decision most likely to be made on Tuesday, October 19.
It comes as Micheál Martin said the lifting of restrictions on Friday week “cannot be guaranteed.”
The Taoiseach was speaking after an ominous briefing from NPHET officials on Wednesday where they warned the path of the pandemic had become increasingly precarious.
Mr Martin told reporters in the Courtyard of Government Buildings on Wednesday evening that the battle against Covid has now “taken a wrong turn.”
And he said the big numbers in recent days - over 2,000 again on Wednesday - were “a matter of concern.”
Mr Martin said: “There was a meeting of senior officials this morning chaired by my Secretary General and the presentation from Deputy Chief Medical Officer, Dr Ronan Glynn, was a serious one.
“The trajectory of the disease has taken a wrong turn.
“There has been a surge, what’s been described as a sudden increase in the last week in terms of case numbers.”
The Taoiseach was asked directly if this meant if it was “fair to say that you can’t guarantee October 22nd reopenings will go ahead.”
And he replied: “I can’t guarantee right now, but we have to wait for further presentations from NPHET, but no decisions were made or anything like that.
“There was a meeting this morning, these issues were raised, presentations were made to officials and I received a briefing on that later this afternoon in terms of the growth of the pattern of the disease and affecting all age groups at this stage.
“So that is a matter for concern.”
The Taoiseach’s comments came in the context of another bad day for Covid numbers, with numbers hitting 2,066 for the day, with 408 in hospital with the disease.
A senior Government source has said the Government is taking NPHET’s warnings seriously but they are not “jumping to conclusions” regarding restrictions.
The source told the Irish Mirror: “We’re just urging people to get back to following the basic public health measures.
“Fresh data has shown complacency has dropped and there is a drop in people sticking to the standard public health measures.
“There has been no real dramatic change but NPHET were warning officials that Covid cases are on the rise and the numbers have gone up.
“The message to people is if you are not vaccinated, please get vaccinated.”
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