Zardari's nomination is also mired in wrangling between the PPP and coalition partner the PML-N over reinstating judges deposed by Musharraf.
Nawaz Sharif, the PML-N leader, said after a PPP delegation approached him for support: "It had been agreed that when Musharraf would resign or get impeached, judges were to be reinstated automatically within 24 hours.
"We have asked them to tell us by Saturday night whether or not judges can be restored on Monday."
Analysts say the PPP is reluctant to restore the judges because of concerns the deposed chief justice might take up challenges to an amnesty from corruption charges last year granted to Zardari and other party leaders.
Sharif also demanded that Zardari slash presidential powers instituted under Musharraf to dissolve parliament before he will support him as a candidate.
"It looks as if the high-stakes poker game is now coming to an end and Pakistani politics is going to be in a period of turmoil again"
Shuja Nawaz, political analyst and author
Shuja Nawaz, a political analyst and author of the book Crossed Swords: Pakistan, Its Army, and the Wars Within
, told Al Jazeera that making those changes "is going to probably take some time and may in fact be the final straw that breaks this coalition's back".
He said: "It looks as if the high-stakes poker game is now coming to an end and Pakistani politics is going to be in a period of turmoil again because, quite clearly, the coalition is now going to split apart at the seams."
"He [Zardari] will have to strengthen his base, he will have to form new alliances, [and] form new coalition partners, including perhaps with the former party of President Musharraf."
Zardari won the unanimous backing of PPP legislators on Friday, hours after Pakistan's election commission announced the date of the presidential poll.
Kanwar Dilshad, the election commission secretary, said nomination papers for the presidency can be filed from August 26, with the final date for any withdrawals on August 30.
No other candidate has yet declared an intention to stand.
Under Pakistan's constitution, a president is elected by members of the country's four provincial assemblies and the national parliament within 30 days of the post becoming vacant.