Nigerian President Muhammadu Buhari will remain in the U.K. to complete medical tests, his office said in an e-mailed statement.

Buhari, 74, was scheduled to return to Nigeria on Sunday and resume official duties on Monday, having left on January 19 for a vacation during which he would undergo unspecified medical tests. Vice President Yemi Osinbajo has been acting president.

Buhari "was advised to complete the test cycle before returning," his spokesman Femi Adesina said in the statement, which didn’t elaborate on the type of examinations he’ll undergo. It also didn’t say when Buhari is expected to return to Nigeria. In June, the president traveled to London to seek treatment for a "persistent ear infection."

Elected in March 2015, Buhari has faced growing opposition to his rule of Africa’s largest oil producer. Last year, he presided over a collapse in the naira to record lows and what’s expected to be the West African nation’s first full-year recession in a quarter century.

That’s led some of his ruling-party members to consider forming a new party to challenge him if he seeks re-election in 2019.

A civic-group coalition known as Enough Is Enough has called for protests Monday in the capital, Abuja, and the commercial capital, Lagos, against worsening economic conditions under Buhari’s administration.

Buhari is currently not in a hospital but at the Nigerian diplomatic residence in London and isn’t facing any serious health problem, Lagos-based This Day newspaper reported another presidential spokesman, Garba Shehu, as saying.

Agencies