Fianna Fáil leader Micheál Martin has insisted the televised election debates should be between himself and Leo Varadkar.
His comments come amid demands from Sinn Féin, buoyed by recent strong opinion poll showings, to be included in the two set-piece debates on RTÉ and Virgin Media One.
"I don't think we should be deciding these issues on opinion polls," Mr Martin said on a visit to Longford.
"I said last Sunday that there would be an opinion poll this week and it would very much be different to the opinion poll we had at the weekend, and we'll have other opinion polls that will be different as well.
"The only two parties that can lead a government in my view are Fine Gael and Fianna Fáil. The only party that can actually lead an alternative government is Fianna Fáil - we're the only party that can bring about a change of government, with other parties (junior coalition partners) I acknowledge.
"And I think it is legitimate that there would be a head-to-head debate between myself and Leo Varadkar in terms of putting an option to the people in terms of the type of governments we would lead."