A panel probing fraud claims in the Afghan election has found Hamid Karzai did not gain enough valid votes for an outright win, the BBC understands.
Preliminary results from August's first round had placed Mr Karzai comfortably over the 50% plus one vote threshold needed to avoid a run-off.
But the BBC understands Mr Karzai's vote share has fallen below half, after a number of votes were ruled invalid.
Under poll rules, Mr Karzai now faces a runoff against rival Abdullah Abdullah.
The panel said it had found "clear and convincing evidence of fraud" at the polling stations, which were across the country.
It was not clear how Mr Karzai would respond to the ECC findings, amid reports of a possible legal challenge.
Initial results released last month had given him nearly 55% of votes, with former foreign minister Mr Abdullah on 28%.
The Afghan president has insisted he won the election outright, but EU observers have said as many as one in four votes cast were suspicious.
Sources have told the BBC that Mr Karzai is furious over the prospect of a second round.
It makes Rahm Emanuel's comment that we must know if we have a partner in Afghanistan before making a decision on troop escalation that much more pointed and the Republicans pressuring Pres. Obama to make a quicker decision regarding Afghanistan that much more ridiculous and reactionary.