The Real Betis forward sustained the injury to his right knee during Sunday's 1-1 draw against Norway in a pre-tournament friendly and had to be helped off the pitch.
"Everyone is waiting for Ezzalzouli's test results to determine the severity of his injury and to know if he'll recover in time for the World Cup," said the source.
Morocco play five-time world champions Brazil in their opening match in East Rutherford on Saturday. They will also face Scotland and Haiti in Group C.
According to the source, team officials "need to wait 48 hours to know the details of the injury before taking a decision."
However, reports of Ezzalzouli being sidelined for three to four weeks, or even missing the World Cup entirely, were dismissed as "speculation".
Morocco also have concerns over the fitness of Manchester United defender Noussair Mazraoui, who hurt his shoulder in the game against Norway.
FIFA World Cup 2026
The 2026 World Cup will be held from June 11th to July 19th in the United States, Canada and Mexico. The tournament will feature 48 national teams and will be played in 16 modern stadiums.
Match schedule and times | Group tables | England at the World Cup | Scotland at the World Cup | Team rosters at the World Cup | How to watch the World Cup | Predictions and odds | Which teams could be considered dark horses?