The Ligue 1 club have already been rocked by the long-term injury to rising star Nabil Fekir, and it has now been announced that academy graduate Kalulu is suffering from a severe sprain and ligament damage.
"Olympique Lyonnais announces that Aldo Kalulu sustained an injury to his left ankle in a clash in training this morning," read a statement on the club's official website earlier in the week.
"The young France U18 international underwent several examinations that revealed he is suffering form a severe sprain to his syndesmosis and a tear to the internal ankle ligament.
"Aldo Kalulu will have a cast put on his ankle on Thursday and will be unavailable for around two months."
Lyon currently hold sixth spot in the league standings after 10 games played.