Joseph Estrada must answer corruption complaints within a week or face formal charges and possible arrest.
Investigators in the Philippines have rejected his request for 30 more days to address the inquiry.
Estrada's deadline was originally set for today but ombudsman Aniano Desierto, who heads government corruption investigations, said Estrada received an automatic extension until February 12.
Mr Desierto said his office will file the corruption complaint less than a week after the new deadline unless Estrada, ousted by street protests on January 20, defends himself in an affidavit to his office.
Without Estrada's defence, he said, the court would probably file formal criminal charges based on the prosecutors' evidence alone. An arrest order would be likely on the same day.
"There is enough evidence to warrant a court case already unless there is something else in (Estrada's) affidavit," said Mr Desierto.
He said that if Estrada files a formal defence prosecutors would have five days to counter. The case would then proceed to court.
Estrada is under investigation on six charges - economic plunder, misuse of funds, violations of the anti-graft law, perjury, bribery and possession of unexplained wealth.
Lawyer Renee Saguisag, a friend of Estrada, warned of unrest and street rallies if Estrada is arrested.
"The emotions it will arouse may lead to something we cannot control," she said. "He has a following that will not agree that the present government is legitimate."