The Socialists are front runners for the election but may not win enough seats to govern on their own.
Spanish Prime Minister Pedro Sanchez said on Tuesday his Socialist party did not intend to include the center-right Ciudadanos in any governing alliance if his party wins Sunday's national election.
"Entering an alliance with a party that has put cordon sanitaire around the Socialist Party is not part of my plans," Sanchez said at the start of Tuesday's second televised debate between himself and three other party leaders.
Ciudadanos, or Citizens, has previously said it will not join any coalition led by Sanchez, and its leader Albert Rivera - together with Conservative Partido Popular's (PP) Pablo Casado - renewed the two-pronged attack they had directed at the prime minister on Monday.
The main contenders in Spain's parliamentary election traded verbal blows over jobs and national identity on Tuesday,
The election is the country's most divisive in decades and, with no single party close to winning a parliamentary majority, its outcome is uncertain. Polls have shown that up to four in 10 voters have yet to decide whom to cast their ballot for.
Sanchez looks best placed to form a government if his Socialist Party wins around 30 percent of the vote that surveys have suggested.
But he would need to team up with one or more parties to form a parliamentary majority, and on Tuesday he distanced himself from one option.
The economy made a late appearance as an election topic in a wide-ranging and at times chaotic debate that also took in immigration, housing and gender equality.
But as on Monday, one of the most emotive issues remained Catalonia and the region's botched 2017 independence bid, which came close to triggering a constitutional crisis.
Casado called Sanchez "the favorite candidate of the enemies of Spain" and Rivera told him: "Many Socialists are disappointed with you because you want to liquidate Spain."
Sanchez, who became prime minister in June, has been more open to dialogue with Catalan separatists than his conservative predecessor Mariano Rajoy.
But he reiterated on Tuesday that he was ruling out any moves toward independence for the region, and that its pro- and anti-secessionist factions needed to negotiate with each other.
The rightist candidates also attacked Sanchez over unemployment. Casado compared Spain's economy to thrice bailed-out Greece and Rivera called the country "the European joblessness champion."
The jobless rate remains above 14 percent.
"This country's problem is short-term employment," said Pablo Iglesias of far-left Unidas Podemos.
Publication of official opinion polls ended six days before the election and in Monday's final survey, by GAD3 in ABC newspaper, the Socialists scored 31.5 percent of the vote, giving Sanchez far more leeway than others to pitch for coalition partners.
However, he may well need to bring separatist lawmakers on board, which would complicate any broader alliance.
A putative coalition of PP, Ciudadanos and the far-right Vox of Santiago Abascal scored a combined 45 percent - putting them short of a parliamentary majority.
Vox was not invited to the debate as it is not currently represented in Spain's parliament.