The former Wimbledon player and television personality was arrested and held for two days because he was involved in a scam to sell land that wasn’t for sale, The Sun UK reported.
Fashanu was released on July 19 on bail.
According to the Mirror, police turned up at his home in the capital Abuja and was arrested on suspicion of “criminal conspiracy.”
It is believed that the 54-year-old pocketed £23,000 in the dodgy scam after acting for a friend who was looking to buy land.
Fashanu has reportedly agreed to pay back the money but has denied any wrongdoing.
A friend of the former footballer told the Mirror: “This is a business deal between friends that has gone south and the police were asked to basically mediate.
“It will all be sorted very quickly. It was a just a business deal.”
Fashanu was forced to surrender his British passport and pay the money back in instalments ahead of his release.
General Hyacinth Dagala, a Nigerian police Deputy Inspector, said: “John Fashanu was arrested on July 17 in connection with an allegation of criminal conspiracy and obtaining the sum of N9,550,000 [Nigerian Naira] under false pretense.
“He was granted administrative bail on July 18 but because of his inability to produce the requisite surety on that day, he remained in detention until July 19 when he was released.”
Fashanu, who has featured on I’m a Celebrity Get Me Out of Here!, had spells at Norwich, Lincoln, Millwall, Wimbledon and Aston Villa.
He went onto co-host British television show Gladiators in the 1990s.