Police say a man pretending to be a solicitor for 15 years is to be charged to court for impersonation on Friday.
The 49-year-old man was arrested earlier this week as he was making a bail application for his client in a Lagos State court.
Police spokesman Chike Oti told the BBC the man could not articulate his legal argument and was challenged by another lawyer present in court.
The suspect, who is due to appear in court on Friday, has not commented.
Mr Oti said the man had been practicing for the past 15 years undetected.
Working with lawyers, the man had some “elementary knowledge of how they [lawyers] go about their business – but he’s not a professional”, the police spokesman told the BBC’s Newsday programme.
Suspicions about his qualifications arose during court proceedings in a criminal case on Tuesday.
His client “was granted bail on the stringent condition, and he wanted a variation of the condition. And he [the suspect] did not know how to go about it”, Mr Oti said.
He added that a lawyer present in the courtroom immediately challenged the suspect, saying that a bar-registered lawyer should be able to deal with a bail issue.
Local media reports say police later questioned the man, who said he had studied law at a Ukrainian university – but had yet to be called to the bar in Nigeria.
Despite this, he has reportedly won several court cases.