It concerns the superstar and former Barcelona player Abde Ezzalzouli. The 24-year-old winger, who now plays for Seville club Real Betis, has made 37 international appearances.
Ezzalzouli injured his knee during the friendly match against Norway this weekend.
Morocco will also have to do without defender Nayef Aguerd, who plays for Marseille.
They have been replaced by Amine Sbaï from French club Angers and Marwane Saadane, who plays for Saudi club Al-Fateh.
Morocco begins the World Cup against Brazil on Sunday night, local time in Sweden.
