The club said on their official website that Moawad, a key member of Ahli's starting line-up, injured his calf while warming up before his side's 1-0 league victory over Wadi Degla.
"Moawad will undergo scans tomorrow to determine the extent of the injury," the Red Devils added.
"The scans will show whether he strained his calf muscle or tore it.
"He will miss the Esperance clash in the first leg of the Champions League semi final if the injury turns out to be a calf muscle tear."
Ahli coach Hossam Al-Badri will be facing an anxious wait to learn whether the influential Moawad would be available for the crunch tie.
The 31-year-old Egyptian international can be hardly replaced following the summer departure of Angolan winger Gilberto.
His understudy, youngster Ayman Ashraf, did not shine in his few appearances with Ahli and his lack of experience might not help him against Esperance.
Ahli could also miss Egypt forward Geddo, who is nursing a knee injury he sustained in last Sunday's 4-2 Champions League defeat at bitter rivals Ismaili.