Nigerian President Muhammadu Buhari, 78, will leave for London on Tuesday for a "routine medical check up" his spokesman said, following concerns about his health.
Mr Buhari visited London several times for check-ups between May 2016, when he was first elected, and 2017 for an undisclosed ailment.
The former general simply said he had "never been so ill" and that he had received several blood transfusions.
Mr Buhari's spokesman said the president would meet "security chiefs first in the morning" on Tuesday before leaving for Britain.
"He is due back in the country during the second week of April," his office said.
Mr Buhari's health became a subject of debate in the last election in February 2020 when the opposition claimed he was not physically fit to govern, but he won a second term.
The president's state of health became a sensitive subject in Nigeria after former leader Umaru Musa Yar'Adua, died in 2010 and it emerged that his ailment had been kept secret for months.