A Nigerian High Court in the capital, Abuja, has found the campaign leader for high-profile presidential candidate Peter Obi guilty of money laundering.
Doyin Okupe was, among other charges, convicted of receiving over $400,000 (£330,000) from an individual without following the correct procedures.
This is likely to deal a major blow to the presidential campaign of Mr Obi.
He has presented himself as a break with previous leaders and parties tainted by corruption.
The elections are due in just two months’ time. Okupe is the director-general of Mr Obi’s campaign organisation and a key ally.
Nigeria’s anti-corruption agency, the Economic and Financial Crimes Commission, had charged Okupe in 2019 for money laundering and diversion of funds.
This was before he began working for Mr Obi. He was accused of accepting money in 2015 in excess of the amount that is allowed without having to declare it to the authorities.
Delivering the judgement on Monday, Justice Ijeoma Ojukwu said that Okupe had violated the Money Laundering Act, and sentenced him to two years in prison – though there is the option to pay a fine.
Neither Okupe’s lawyers nor the Obi campaign have yet reacted to the judgement.
Mr Obi is running without the backing of either of Nigeria’s two main political parties but he has cultivated a lot of support among young people.
Mr Obi is among a field of 18 candidates, including Bola Tinubu of the governing APC and Atiku Abubakar of the PDP – the country’s two main political parties.