Mensah was detained in suspicion of a car theft, but was released after police forces conceded that the 27-year-old, who does not speak French, was a victim of a misunderstanding.
However, Mensah is struggling to get over the incident, which forced to lose concentration in football.
"I was arrested and told to get out of the car; I didn’t understand what was happening. They treated me like a criminal before putting me in custody and then freeing me," the Lyon defender told L'Equipe.
"They didn’t even ask me for my papers. I did nothing illegal and I was not in a speeding situation.
"This was the worst moment of my life since I have come to France.
"It made me lose all my concentration, that’s why I couldn’t play the matches against Fiorentina and Le Havre."