Ezzalzouli was replaced at half-time of Morocco's final World Cup warm-up game against Norway on Sunday, and Manchester United full-back Noussair Mazraoui also departed in the 29th minute with a shoulder problem.
Morocco's head coach Mohamed Ouahbi was "concerned" about the extent of the injuries during his post-match interview, and there is sadly bad news for Real Betis winger Ezzalzouli.
According to journalist Hanif Ben Berkane, the Betis superstar has sprained his internal knee ligament and is likely to miss the World Cup.
A three to four-week recovery is expected for the 24-year-old, who was poised to star at the prestigious tournament after an incredible campaign in Spain.
The 37-cap Moroccan plundered 15 goals and supplied 13 assists in all competitions, becoming one of the finest talents in LaLiga and drawing transfer attention in the process.
Newcastle United have scouted Ezzalzouli as a possible replacement for Anthony Gordon after he joined Barcelona for £70 million.
Morocco kick off their World Cup campaign with a showdown against Brazil on June 13 as they look to emulate their success in 2022 after becoming the first African team to reach the semi-finals.