ABUJA (Reuters) - President Muhammadu Buhari asked parliament on Sunday to extend his medical leave, his office said in a statement, deepening suspicions among many Nigerians that his health is worse than officials are admitting publicly.

FILE PHOTO - Nigerian President Muhammadu Buhari speaks during German President Joachim Gauck's visit to the State House in Abuja, Nigeria February 11, 2016. REUTERS/Afolabi Sotunde/File Photo

The statement did not say how much extra time Buhari was seeking off. He had been due to return to work on Monday after taking more than two weeks’ leave for medical checks in Britain.

“President Muhammadu Buhari has written to the National Assembly today, February 5, 2017, informing of his desire to extend his leave in order to complete and receive the results of a series of tests recommended by his doctors,” Sunday’s statement said.

Buhari’s extended leave could further erode confidence in his administration, already under pressure from investors to let Nigeria’s currency float freely to try to revive an oil-driven economy now is at its weakest in 25 years.

Meanwhile, in the northeast, a humanitarian crisis threatens millions, ridden by conflict with Islamic insurgents Boko Haram.

The president “is not in any serious medical condition,” said Buhari’s spokesman Garba Shehu by phone, adding there was no expected date for Buhari’s return. He declined to give details of the medical checks.

Some Nigerians took to social media demanding more details on the president’s health.

“If Buhari isn’t healthy enough to be president, he should resign and go and rest with his family,” said Twitter user @Flappizy.

As rumors swirled last month that Buhari was gravely ill, his office urged Nigerians to disregard what it said were false and subversive messages.

Buhari also spent nearly two weeks in London last June for treatment for an ear infection, stoking concerns for his health now.

Buhari’s predecessor, Goodluck Jonathan, was sworn in after the death in 2010 of President Umaru Yar’Adua. His illness created a power vacuum that was filled by Jonathan, his vice president, only after three months of political infighting.