The Fianna Fáil leader Michál Martin has said he thinks Leo Varadkar and Fine Gael will run an 'attack dog' style election campaign.
It comes as speculation continues to mount that we could see a general election in early 2020, with the Fianna Fáil and Fine Gael leaders are expected to meet in January to discuss potential dates.
Ahead of that meeting, Deputy Martin suggested we have seen "negative tactics emerge" in politics recently.
The Fianna Fáil leader argued: "Fine Gael has said this, they've trialed this... that they're going to go for Fianna Fáil frontbench people, they're going to go for me.
"That's going to be attack dog approach - that's what I mean by the nasty side of politics coming out."
Mr Martin also compared the Taoiseach's approach to that of British Prime Minister Boris Johnson - stressing that's 'certainly not' a compliment.
He argued: "Boris Johnson [promised] 40 hospitals - I think about three or four of them are realistic prospects.
"I note now that we're going to get promises for ten years time - everything is couched in that kind of language."
Deputy Martin also suggested Leo Varadkar has been attempting to "deflect" issues his own party has been experiencing, including those around former TD Dara Murphy and their now deselected Wexford candidate Verona Murphy.
His remarks come as the Taoiseach said he'll meet with the opposition leader early in the New Year, amid continued speculation over a potential election date.
Mr Varadkar - who has previously said he'd prefer an election in May - has clearly hinted that a general election date is likely to be announced sooner rather than later.
He argued: "What I don't want to see is a three or four month election campaign, and the Dáil and the Government effectively focusing on that rather than focusing on the business of government and dealing with the problems people face in their everyday lives.
"That's what we're supposed to do, that's what we're paid to do, and that's what we should be doing."
