The injury was sustained while training by the former WAFA star, who has subsequently had successful surgery.
Horneland verified Boakye's absence prior to Saint Etienne's pivotal game against Paris Saint-Germain (PSG), the leaders of Ligue 1.
The Norwegian coach said, "He had surgery during the international break and will be out for the rest of the season."
With three goals in 17 games this season, Boakye, 24, has been a vital member of Saint Etienne's squad. In addition to Nathaniel Adjei, Alidu Seidu, and Fatawu Issahaku, his injury brings Ghana's list of long-term absentees to an increasing number.
Currently facing relegation, Saint Etienne is in a desperate attempt to salvage their season.
They have lost their last nine games and will have a difficult time this Saturday against an undefeated PSG team.
Currently facing relegation, Saint Etienne is in a desperate attempt to salvage their season.
They have lost their last nine games and will have a difficult time this Saturday against an undefeated PSG team.