Egypt left-back Ahmed Fatouh limped off with a worrying injury against South Sudan on Tuesday evening at Juba Stadium, in the second round of Group Two of the 2027 Africa Cup of Nations qualifiers.
The full-back signalled to coach Hossam Hassan in the 52nd minute after hurting the front thigh muscle in a challenge for the ball. Karim Hafez came on in his place.
Medical examinations over the coming hours will diagnose the problem and reveal how long he faces on the sidelines.
For Zamalek coach Moamen Gamal, the timing could hardly be worse. Fatouh is a key figure in his side both in the league and the CAF Champions League.
Waiting for Zamalek is a bruising test against arch-rivals Al-Ahly at the summit of the Egyptian league on 11 October.