If the anti-establishment Five Star Movement party seizes power in the election, it will hold a referendum on Italy’s membership of the eurozone.
This would pave the way for quitting the euro, plunging the eurozone into chaos and leading to the disintegration of the EU.
Simon Tilford, deputy director of the Centre for European Reform (CER), said that an Italian referendum on the eurozone would lead to considerable instability in Europe.
Comedian Beppe Grillo is the founder of the Five Star Movement
The latest polls show that Italy is set to reject the establishment by voting no in the constitutional reform referendum next week.
But Mr Tilford said that Mr Renzi might not resign as promised because he has qualified his original pledge to do so.
He added: “It looks like he is going to lose but we have got no idea if he will hold on to power or honour his original commitment by resigning.
“If he hangs on, he might manage to ride the fallout until the next election.”