Fitch Ratings on Jan. 25 revised the outlook on Nigeria's long-term foreign- and local-currency issuer default ratings to negative from stable, while affirming them at B+.

Fitch estimates GDP growth of negative 1.5% in 2016, with a 1.5% growth in 2017, well below the 2011-2015 annual growth average of 4.8%.

Fitch said that access to foreign exchange will remain severely restricted until the Central Bank of Nigeria can establish the credibility of the interbank foreign exchange market and reduce the spread between the official rate and parallel market rates. Some Nigerian banks even struggled to meet their trade finance obligations due to tight foreign-currency liquidity, which will continue to constrain the non-oil economy, Fitch said.

The rating agency noted that gross general government debt increased to an estimated 17% of GDP at 2016-end, from 13% at the end of 2015, adding that the country's low revenues pose a risk to debt sustainability.

Meanwhile, Fitch highlighted the Nigerian banking sector's worsening asset quality levels due to the deteriorating economy, problems in the oil industry and exchange rate pressures on borrowers to service their loans.