The left-sided Swiss midfielder, 33, suffered the injury to his right shoulder in the first half of the Ligue 1 match against Sochaux on Saturday.
Evian won that match 5-1 to leapfrog Sochaux on goal difference, pushing their relegation rivals into the bottom three.
Ehret was already suspended for their next two matches, against Lille and Reims, after retrospectively being found guilty of a dangerous challenge on Marseille’s Andre-Pierre Gignac.

