Piotr Müller made the declaration in a media interview a day after Morawiecki was given a chance to form a new government, Polish state news agency PAP reported.
The government spokesman told private broadcaster Radio Plus on Tuesday: "Mateusz Morawiecki has 14 days to name his new Cabinet. It will likely happen within the next 12 to 14 days."
Polish government spokesman Piotr Müller. PAP/Leszek Szymański
Polish President Andrzej Duda on Monday named Morawiecki as prime minister-designate, tasking him with forming a new Cabinet.
The 14-day deadline means Morawiecki has to unveil the new government by November 27.
Müller said on Tuesday that the ruling conservative Law and Justice (PiS) party "seeks to form a Cabinet that has a different composition from the current one."
The government spokesman added that the president's decision to give Morawiecki a chance to form a new Cabinet was "fair" as his Law and Justice party had won last month's election.
Müller said the PiS party had "a duty to try and form a new government," even though a coalition of pro-European Union parties now had a majority in parliament and will likely assume power, Polsat News reported.
Poles elected a new set of 460 MPs and 100 senators when they went to the ballot box last month.
Morawiecki's ruling conservatives won Poland's October 15 election, but lost their parliamentary majority and look unlikely to stay in power for a third consecutive term.
A bloc of pro-EU opposition parties on Monday secured a resounding victory in Poland's new parliament during its first key vote to elect a house Speaker.
Poland's pro-European opposition groups on Friday signed an agreement to form a coalition government, pledging to restore the rule of law, promote green energy and relax abortion rules, among other policies.
(pm/gs)
Source: PAP, Polsat News