Jarosław Kaczyński made the declaration in an interview with state PAP news agency, published on Friday morning.
He said that Morawiecki's effort to form a new government, following last month's parliamentary election, would be "very difficult," but "not doomed."
Kaczyński, who serves as deputy prime minister, added that the attempt to assemble a new coalition Cabinet would be "based on facts, on the situation in the European Union."
He said his Law and Justice party would "appeal to the real interests of political groupings," which "don't have to align with the interests of the Civic Coalition," the biggest opposition bloc.
Kaczyński added that "the final decisions about what would be in line with the interests of individual parties would be made by their leaders."
The Polish conservative leader noted that Morawiecki's proposed new government "may not get a vote of confidence from parliament."
Kaczyński said his party "must be ready for every scenario" and "in that case," it already has "a plan for being in opposition."
Referring to the election results, Kaczyński said Law and Justice had "won a good victory," despite failing to get a majority of 231 seats in the lower house, the Sejm.
Kaczyński also said that his party would "analyse" why it failed to win a parliamentary majority, the PAP news agency reported.
Poland set to appoint new gov't
Poland’s ruling conservatives won the parliamentary election on October 15, but lost their majority to an alliance of four pro-EU opposition parties led by the liberal Civic Coalition (KO).
President Andrzej Duda announced on Monday that the task of forming a new government would be given to Morawiecki.
As all other parties have ruled out entering into a coalition government with Morawiecki's Law and Justice, the current ruling party, in power since 2015, looks unlikely to be able to govern.
If Morawiecki is unable to win a vote of confidence in the lower house, the chamber will appoint another prime minister.
The job is expected to go to former top EU official Donald Tusk, who has been named by the four opposition parties as their choice for the next head of government.
Tusk was Poland's prime minister from 2007 to 2014.
(pm/gs)
Source: PAP