Mansouri began his career at Tinqueux SC, a small team from Tinqueux who were playing in the sixth division. At age 17, he left the club and signed with Le Havre AC who were playing in Ligue 1, where he spent his first two seasons playing in the reserve side. He made his debut in the first game of the 1997–1998 season, coming as a second half substitute against Olympique de Marseille. He would slowly assert himself at the club and would eventually go on to make 134 appearances and scoring 2 goals in 6 seasons in both Ligue 1 and Ligue 2.