Nigeria's President Muhammadu Buhari is recuperating quickly, his wife Aisha Buhari said earlier this week after visiting him in the UK. Buhari, 74, is on medical leave in London, for the second time since the beginning of 2017.

Before leaving both times, the leader handed over powers to Vice President Yemi Osinbajo, amid calls for the president to step down, as some see him unable to continue to lead a country marred by corruption, economic recession and terrorism.

The first lady's remarks echoed those of a Nigerian official in London who said in May that Buhari's health was improving "significantly."

However, the leader's medical trips, and mystery surrounding his medical condition, are sparking speculation about his health and the future of one of Africa's largest economies.

Here is a look at Buhari's troubled health since the start of the year:

19 January: Buhari leaves to the UK for a 10-day vacation.

6 February: The leader fails to return to Nigeria and prolongs his stay to complete medical tests recommended by doctors.

21 February: Staff at Abuja House in west London refuse to provide any updates on Buhari's health when IBTimes UK arrives at the government-owned building.

22 February: Buhari needs more time to rest, his spokesperson says. President of Nigerian senate, Bukola Saraki, travels to London to visit the leader twice.

10 March: Leader goes back to Nigeria after nearly two months on medical leave. Upon return, he says he "has never been so ill".

26 April: Buhari misses two consecutive cabinet meetings and officials say he works from home and at a slower pace as he is still recuperating.

28 April: The head of state misses Friday prayers.

3 May: Buhari misses third consecutive cabinet meeting as rumours of a second trip to the UK emerge.

5 May: He appears at Friday prayers in the federal capital of Abuja, but concern due to his apparent deteriorating health remains

7 May: Buhari travels back to the UK for further treatment. "Tonight I leave for London, to see my doctors. When I came back in March, I hinted that there might be a need to return soon, for a follow-up. I'd like to assure all Nigerians that there is no cause for worry," the president writes on Twitter before his departure.

18 May: Fears of a possible coup emerge after military warns it received information that "some individuals have been approaching some officers and soldiers for undisclosed political reasons". Analysts tell IBTimes UK a coup is possible but unlikely. However, there are fears politicians loyal to Buhari, a Muslim from the north, could obstruct Osinbajo, a Christian from the south.

24 May: Director of Defence Information, John Enenche, says the army remains "totally loyal" to Buhari.

6 June: Aisha Buhari says Buhari is "recuperating fast". A return date has not been set.

10 June: Reuters quotes presidential sources as saying leader will not go back to Nigeria at the weekend (10-11 June) as he needs to undergo further medical tests. Sources said tests results will determine when the leader can return to his homeland.

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