The young midfielder faces a lengthy spell on the sidelines following the sustaining of a serious knee injury during a training session
The 23-year-old has appeared seven times for the French champions this campaign, but he will have to wait until April at the earliest before he makes a return to action.
"The verdict is in after the medical examination," Ait-Fana announced on his personal Twitter account.
"I've ruptured my anterior cruciate ligament and will be out for six months."
Ait-Fana has already featured in the Champions League for La Paillade, scoring a goal in his side's 2-2 draw with Schalke earlier this month, and his absence will be a blow to the club's hopes of progression.
Montpellier are currently 15th in Ligue 1, and will hope to pick up their form when they face Stade Rennais on Saturday.