Nigeria's president has another medical consultation in Britain and it is not known how long he will be gone.
Nigeria's president will undergo further medical tests in London, renewing fears over his health after he spent weeks overseas on medical leave earlier this year.
The announcement came shortly after 74-year-old President Muhammadu Buhari met the 82 Chibok schoolgirls freed this weekend from three years of captivity by Boko Haram extremists.
The latest medical leave startled Africa's most populous nation even as it rejoiced in the schoolgirls' return.
Buhari has missed three straight Cabinet meetings and is said to spend most of his time working from home. On Friday, the government released images of his first public appearance in a week as he attended Friday prayers.
The nature of the president's illness remains unclear. On his return from his earlier medical leave in London in March, Buhari made reference to blood transfusions.
That earlier absence led some to call for Buhari's replacement.
Photos from his meeting with the freed schoolgirls on Sunday night showed the rail-thin leader standing and addressing his audience.
A statement from the president's office said Buhari had delayed leaving for London earlier Sunday so he could meet with the schoolgirls.