The 64-year-old has been at the head of the Montbeliard club since December 1999 and has seen them win three trophies - the Ligue 2 championship in 2001, the Coupe de la Ligue in 2004 and the Coupe de France last season.
Alain Cordier is expected to take over Plessis´ duties from the start of next season.
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