Calls for Yar'Adua, a northern Muslim, to step down or transfer power to Goodluck Jonathan, a southern Christian, have mounted in recent weeks.
Yar'Adua left the country on November 23, last year, for Saudi Arabia without notifying the National Assembly or designating Jonathan to take over in his absence.
His absence has plunged Nigeria into its most serious constitutional crisis since the end of 33 years of military rule in 1999.
Since Yar'Adua left, nearly 150 Nigerians have been killed in clashes between Muslim and Christian groups in the capital of a central state, Jos, and a Nigerian was charged with trying to bomb a Detroit-bound Northwest Airlines plane.
The opposition has claimed his continued absence has stalled business decisions and threatens the fragile peace process in the Niger Delta, where western oil companies pump the bulk of Nigeria's crude. Economic decisions -- including the controversial withdrawal of fuel subsidies, a radical oil industry bill, and getting the 2010 budget through parliament -- are awaiting action by the president.
Yar'Adua's refusal to release his grip on power and hand over to Jonathan could derail the peace process in the Niger Delta. The president led the secret peace talks with militant leaders and stakeholders, which restored peace in the region and boosted oil production, but negotiations have stalled.
Nigeria's most armed group, the Movement for the Emancipation of the Niger Delta (MEND) dealt a severe blow to peace efforts last month after it claimed responsibility for an attack on an oil pipeline because Yar'Adua's absence was delaying peace talks.
Nigeria's Federal High Court on Friday gave the cabinet 14 days to decide if Yar'Adua was fit to stay in office. Judge Dan Abutu directed the cabinet to resolve whether the president "is incapable of discharging the function of his office."
Friday's case was one of three separate legal challenges to force the 58-year-old president to swear in Jonathan without delay.
Fourteen days from today makes it 73 days without a president at the helm of Africa's leading oil exporter. Even the president's closest aides have accepted that Yar'Adua may never return as president.
"It is over for this president," said one source. "The question is when and how."

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