The party of assassinated former prime minister Benazir Bhutto, which is set to lead Pakistan's incoming coalition government, will nominate its candidate for the premiership by Sunday.
The Pakistan People's Party (PPP) is led by Bhutto's widower, Asif Ali Zardari, but he is ineligible for the premiership because he is not a member of the assembly.
There is speculation that the PPP will nominate a stop-gap prime minister, and Mr Zardari will move into the slot later. But he will have to win a by-election first.
Ms Bhutto's 19-year-old son Bilawal Bhutto Zardari has returned to Pakistan and is expected to reveal the party's choice. The new prime minister would then be sworn into office on Tuesday.
President Pervez Musharraf has few allies left in the assembly after their defeat in an election on February 18th.
Mr Musharraf, who came to power as a general in a coup in 1999, appears increasingly isolated, and there is intense speculation over how long the US ally will be able to hold onto power.
The incoming government has pledged to pass a resolution to reinstate Supreme Court judges who Mr Musharraf replaced in November out of fear that they could rule unconstitutional his own re-election by the previous assembly.