Mary Lou McDonald will "pick up the phone" and engage with parties of the left, should the programme for government be rejected by either Fianna Fáil, Fine Gael or the Green Party.
The Sinn Féin leader is ready to engage with "pro-change" parties, according to her housing spokesperson Eoin O Broin.
Mr O Broin said today that the idea that there is no alternative to the proposed government was "deeply dishonest way to characterise what is happening" designed to pressure party members into "accepting a bad deal".
Mr O Broin said that in the event of the deal being rejected, his party leader would attempt to form a government.
"There is an alternative if this deal is rejected on Friday. That is that Mary Lou McDonald, in the first instance will pick up the phone and engage with pro-change parties to try to put together an alternative programme for government.
"It is our view that this could be done very quickly and is the right thing to do."
The parties of the left had worked on a programme for government before the Covid-19 emergency had broken out, but the decision by the Greens to enter talks with Fianna Fáil and Fine Gael on government formation saw this end.
Renewed public remarks about restarting talks did not yield a document. A coalition of Sinn Féin, the Greens, Labour, Solidarity-PBP and the Social Democrats would yield just 67 seats, 13 shy of a majority.
Mr O Broin said that if those parties coalesce, "it would be up to Fine Gael and Fianna Fáil" to decide if they would support a government either from opposition or through confidence and supply.
He said that he disagreed with Green Party leader Eamon Ryan that the proposed programme is a "left-wing" document.
"We could have a programme for government for change. But this document is more of the same."
Mr O Broin said that the Green Party's use of actor Mark Ruffalo to support the climate parts of the deal may not decide the vote.
"I'm hearing that the Green vote could be very tight. Whether or not a Hollywood actor - and a very genuine campaigner - will have any sway, I don't know."