Both went off early in Sunday's 1-1 draw with Norway in their last warm-up match before this week's kick-off of the tournament in Canada, Mexico, and the United States.
Ezzalzouli was replaced at half-time after suffering a leg injury, while Mazraoui departed in the 29th minute with a shoulder problem after a tough encounter in which Morocco took an early lead but Norway equalised with 15 minutes remaining.
"We left a good impression despite not winning because we really showed some very good things against a very good opponent," coach Mohamed Ouahbi told reporters.
"That's the point of playing against teams like this. When you make so many changes (10 in total), it's difficult for the player but it was important that we managed everyone's playing time.
"Two players went off injured. We're waiting to see how serious it is. I’m more concerned about that," the coach added.
Morocco were surprise semi-finalists at the last World Cup and have high hopes of another strong performance at the 2026 finals.
They open proceedings in Group D with the clash against the five-time champions at the MetLife Stadium.