Sam McConkey says Ireland needs to take action to tackle rising COVID-19 rates before it's too late, likening it to a frog in boiling water.
It comes as NPHET has said every county should move to the most severe level of restrictions, and return to essentially a full lockdown.
The Government will consider whether to place the country in level five.
Professor McConkey is head of the department of international health and tropical medicine at the Royal College of Surgeons in Ireland.
He told Pat Kenny something needs to be done, but it should be an all-island approach.
"I feel as a nation we definitely need to do something - we can't just be like the frog in the slowly boiling water that stays there and gets boiled over, and then it's too late to jump once it's boiling.
"We've got to take some sort of collective action and it's really up to our Government to take a key decision.
"I hope linking with the people in Northern Ireland [and] that it's a cross-border, coordinated decision.
"And ideally Scotland, England and even other European countries - you've seen other European counties going in similar directions, so I would suggest coordinated action".
He said such an approach would make sense for several reasons.
"There's a lot of essential business that work across the border, like agriculture and food processing, a lot of the cows in the North - their milk is processed partially in the South and then goes back to the North for drying - and then maybe packaged in the South.
"So we've a lot of cross-border essential industries like the agri-business that are really important for the health and wealth of the people in Ireland.
"They're indigenously-owned Irish businesses that are important for feeding us and important for export that are considered essential services.
"So there will be still some cross-border work... I feel important things like shopping for food - whether it's across the border or not - really doesn't make that much difference if you shop for food in Lifford or in Strabane".
'We shouldn't be doing business that way'
While Fianna Fáil TD Jim O'Callaghan says the approach and messaging by NPHET is wrong.
"I'm concerned by the manner at which we're doing business at present.
"It's not a good idea for the people of Ireland to hear late on a Sunday evening a leak from NPHET, indicating that there's a recommendation that the country's going to go to level five.
"We shouldn't be doing business that way.
"NPEHTs job is to advice the Minister for Health, it's job is to coordinate the health sector response to COVID - but it's not an independent entity.
"It's a group that advises the minister, and it's Government and politicians that will make decisions as to whether or not this country moves to a different level".
He said the Government should be asking why there is an inconsistency in NPHETs approach.
"They met last Thursday [and] there was no recommendation in respect of this.
"I'm also concerned that if Government are to go to level five it would be completely disproportionate at this stage.
"We've to look to see where we are in terms of this pandemic... the primary way you do it is you assess it by the number of deaths and you assess it by number of hospitalisations.
"To date, 1,810 people in the country have died of or with COVID and only 47 of them have been recorded as dying since the 1st of August".