Adesina said Buhari would have left earlier on Sunday but wanted to meet the students, who were kidnapped by Boko Haram fighters along with almost 200 others in northeast Nigeria in April 2014, causing worldwide outrage.
On January 19, 2017 Buhari left Nigeria for London to "undergo routine medical check-ups" but returned after nearly two months on March 10.
President of Nigeria, Muhammadu Buhari is leaving the country for London for medical check up, a statement issued by his press aide has said.
For his part, Buhari says "there is no cause for worry", however recent history suggests otherwise given Nigeria lost a sitting president in 2010.
In the letter he sent to the senate and read by Senate President Bukola Saraki on Tuesday, Buhari said the vice president would "coordinate the activities of government" in his absence.
The letter read, "In compliance with Section 145 (1) of the 1999 Constitution (as amended), I wish to inform the distinguished Senate that I will be away for a scheduled medical follow-up with my doctors in London".
Buhari has missed three straight Cabinet meetings and is said to spend most of his time working from home.
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Speaking about what it is like resettling in Canada, Afraa told the BBC : "Canada is much more safe - there's no war, nothing". However, they are thankful to be here, she said, and happy to welcome their first Canadian son.
According to those Senators, the letter was not clear enough, especially as regards the transfer of the powers of his office to Vice President Osinbajo.
When Mr Buhari returned from London in March, he said he had never felt "so sick" as he had when he was being treated and warned that he may have to undergo further medical checks.
Buhari also said he was pleased to have personally met the girls and assured them that the presidency will personally supervise the performance of those entrusted with their welfare.
Investigations by Vanguard, last night, revealed that chairman of the committee, Acting President Yemi Osinbajo would not take any soft measure that may exonerate Lawal and Oke.
Tonight I leave for London, to see my doctors.
The group, at a two day Consultative General Assembly held in Abuja during the week stated that since the president has not told anybody he is unfit to lead, no one should force him out of power.