5-Star's parliamentary party leader Danilo Toninelli told state television Rai: "The only way to get a serious government is to return to the polls".
More than ten weeks after Italy's inconclusive election on March 4, the two politicians are still trying to broker an agreement after repeatedly blowing through deadlines set by President Sergio Mattarella.
The Five Star Movement and League parties were continuing to work on a government deal on Wednesday afternoon, with the leader of the M5S saying he and his League counterpart were prepared not to be part of the government if needed.
For his part, Salvini said being PM would be an "honour" but added "if necessary I will step to the side".
5-Star and the League said in a statement that the draft, which was dated May 14, was "an old version that has been considerably modified".
He also said the only alternative to a deal was another election.
The European Union is meddling in Italy's domestic politics, according to League leader Matteo Salvini.
The 39-page document, obtained by Huffington Post Italia, also calls for a renegotiation of Italy's European Union budget contributions, an end to sanctions against Russian Federation and plans to dismantle a 2011 pension reform that raised the retirement age.
Both Mr Salvini and Mr Di Maio have warned the EU's budgetary austerity is "suffocating" Italy and have spoken out against the bloc's sanctions issued against Russian Federation following the annexation of Crimea and branded unfair for the country the EU's migration rules.
Salvini said that the contract - and an interior minister from the League - would make sure that "only people with a right to enter Italy" would do so. "I'm working right until the end to see whether it will be possible".