The baby lion was discovered inside a hired Lamborghini during a police search on the busy luxury shopping street, according to the source, confirming earlier media reports.
The driver was taken into custody and the cub was being looked after, they said.
Last month, a six-week-old lion cub was seized from an apartment in a Paris suburb and the owner sentenced to six months in prison.
During that trial, the prosecutor said the discovery was not an isolated case and investigations were already underway into three other baby lions kept on the outskirts of the capital.
In a separate incident also in October, a tiny lion cub weighing just a few kilos was found in a car garage in the southern French city of Marseille.
That cub, a female believed to be between one and two months old, has been passed on to a specialist NGO which works to shelter wild animals.