Television footage showed Brazilian Leonardo bumping into referee Alexandre Castro with his left shoulder in the Parc des Princes tunnel after Ligue 1 champions PSG drew 1-1 with Valenciennes in Ligue 1 on May 5.
"The [disciplinary] commission hands him a nine-month ban," the LFP said in a statement, adding that Leonardo was banned from the bench, the referees' dressing-room and from all official functions.
"Paris Saint-Germain considers this decision to be unjustified and extremely harsh. As a result, and in solidarity with its sporting director, Paris Saint-Germain will appeal this decision," PSG said.
"The commission's task was to decide whether the shoulder barge was intentional," commission president Pascal Garibian told a news conference.
"The commission retained this idea. The commission judges acts, players, and people independently of a club's notoriety."
Leonardo, the former Inter and AC Milan manager, received a two-match suspended ban in November from the French federation's Ethics Committee for criticising the referee after Mamadou Sakho was sent off in a league game at Montpellier.
Leonardo's latest suspension is a huge blow for PSG, who are reportedly seeking a replacement for Italian coach Carlo Ancelotti who has said he wants to leave the club.
