Saturday is the deadline Mr Abdullah has set for his "minimum conditions"
President Hamid Karzai's rival in the second round of the Afghan presidential poll says he will announce on Sunday whether he intends to quit the race.
Abdullah Abdullah called for the resignation of key election officials and others as a way to mitigate fraud and corruption in the vote.
But those demands were rejected earlier in the week in talks with Mr Karzai.
A senior adviser said that in talks on Friday, Mr Abdullah's team decided he should not take part in the poll.
But Mr Adbullah's campaign said on Saturday that no final decision had been made, and that the former foreign minister would announce his next move on Sunday.
Hillary Clinton: 'I do not think it affects the legitimacy'
The BBC's Ian Pannell in Kabul says that if he withdraws it will raise serious questions about the credibility of the election.
However, US Secretary of State Hillary Clinton said a runoff with only one candidate would not necessarily threaten the legitimacy of the process.
"We see that happen in our own country where, for whatever combination of reasons, one of the candidates decides not to go forward," Mrs Clinton told reporters in the United Arab Emirates.
'Nothing has changed'
Hundreds of thousands of votes were discounted from August's first round of voting.
The UN-backed Electoral Complaints Commission's (ECC) action meant Mr Karzai's total was reduced to below the 50% plus one vote threshold for outright victory, indicating a run-off poll was needed.
Among the "minimum conditions" Mr Abdullah has set for holding a relatively fair and free contest to be accepted, is sacking of the head of the country's Independent Election Commission (IEC), Azizullah Lodin.
KARZAI V ABDULLAH
First popularly elected president of Afghanistan
Opposed Soviet occupation in 1980s
Critics say he has done little to rein in corruption
Tajik-Pashtun, doctor by profession
Senior Northern Alliance leader during Taliban rule
The deadline for those conditions to be met expires on Saturday.
On Monday, Mr Adbullah said Mr Lodin had "no credibility". Mr Lodin denies allegations that he favoured Mr Karzai.
One of Mr Abdullah's senior advisers, Ahmed Wali Massoud, said he was unhappy that nothing had been done to redress the electoral system's problems.
"The fact is that the infrastructure of this fraud is still there. Almost 1.5 million votes were rigged. Nothing has changed," he told the BBC.
"So if you go back and do the second round election, it means that it will happen again. So, therefore, I don't think that we would be willing to participate."
Earlier, the IEC announced that it planned to open 6,322 polling stations for the run-off - more than it did during the first round.
The ECC had recommended cutting the number from 6,000 to about 5,800 - to make sure there would be enough monitors to limit fraud and troops to ensure security.
Mr Abdullah served as foreign minister in the short-lived government headed by the Northern Alliance, and continued as "foreign minister in exile" throughout the years of rule by the Taliban, which was ousted in 2001.
He continued in that role under the Karzai government that was formed after the fall of the Taliban, leaving the government in 2006.
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