The French League said after a meeting of its disciplinary committee that the sanction would take effect from December 24.
Jeunechamp had already been suspended indefinitely after the argument with a L'Equipe reporter over a story published in the newspaper before the 1-1 league draw at Valenciennes.
The defender punched Jose Barroso in the face after taking offence at a report claiming that the Montpellier players were unhappy with coach Rene Girard.
Jeunechamp is 37 and the suspension may have effectively ended his career.
A statement by the disciplinary committee read: "The commission has decided to hand the player Cyril Jeunechamp a one-year suspension following his acts of brutality on Mr Jose Barroso, which led to Mr Barroso taking sick leave."
Champions Montpellier had apologised to the reporter and condemned their player's behaviour. The club are currently ninth in the 20-strong league.
Owner Louis Nicollin said: "The player said he didn't do anything, the journalist claims he charged towards him.
"I would rather believe the journalist. In most cases, the players are little boys who can't stand the pressure. What annoys me is that the club gets the image of being a gang of louts."