The female cub was discovered in a child's bed in the apartment of neighbours of the 30-year-old suspect, who was found hiding in a closet, they said.
The cub was in good health, and was handed over to wildlife officials.
Police were alerted by videos circulating on social media, in which a man offers the cub for sale for about €10,000 ($11,470), said the source.
It was not known where the lion came from.
The source said it seemed the suspect had bought the cub with the intention of reselling it, and that it was very likely stolen.
Strangely enough, this isn't the first lion cub to have been rescued by Paris authorities.
Last October, a half-starved lion cub was found in an empty apartment in the gritty Paris suburb of Noisy-le-Sec, after the animal was abandoned by a man who 'hired it' to show off.
Fortunately, King's carers were able to find him a new home in an animal reserve in South Africa last August.