Salvini, whose party got most votes in the right-wing coalition in Italy's inconclusive general election, said he would not hesitate to breach EU spending rules if he became prime minister.
The March 4th ballot resulted in a hung parliament with the maverick anti-establishment Five Star Movement (M5S) the biggest party but short of a majority and struggling to find coalition partners.
"The euro is a mistake but I think we cannot plan to leave the euro in an improvised manner," Salvini told reporters at the European Parliament in Strasbourg.
Salvini has claimed he has the "right and duty" to govern Italy, though his coalition with flamboyant ex-PM Silvio Berlusconi's more moderate rightwing Forza Italia party fell short of a majority.
He said if he became the prime minister of Italy, the eurozone's third largest economy, he would not feel bound to stick to the EU's three percent deficit-to-GDP ratio.
Salvini (L) with his allies in the European Parliament, including fellow eurosceptics Marine Le Pen and Geert Wilders. Photo: Emmanuel Dunand/AFP
The limit "is part of the European rules that have been imposed", said Salvini, who is leaving his role as an MEP to take up a seat in the Italian parliament.
"If it's possible [to follow the rule] I will do it, but if respecting the three percent means job losses or social catastrophes, we will not accept it," he said.
The anti-EU, anti-immigrant League wants to renegotiate European treaties and rules which Salvini says have "negative repercussions for Italians".
"If we can't do it, I don't rule anything out but an improvised exit from the euro is not desirable and it's not something we want," he said, adding that his party was working on a "plan B".
Nicolas Bay, an MEP from France's far-right National Front, told AFP they could hold joint events with the League on the campaign trail for next year's European elections.