The 29-year-old sustained a groin complaint during Ahli's 3-0 win over second-division side Nabaroh in the Cup's first round but still played against Zamalek due to shortage of options upfront.
He was fielded as a lone striker against Ahli's arch-rivals and managed to live up to expectations, with his close-range effort giving the Red Devils a 2-1 lead seven minutes before the break.
However, he aggravated his injury but coach Hossam Al-Badri still hopes he will be able to feature in the quarter-final clash against Petrojet.
If Fadl misses out on the game, Al-Badri will have no option but to field one of the out-of-favor duo Ahmed Belal and Liberian Francis Doe.
Ahli's top scorer Emad Meteb, who scored nine goals in the team's triumphant Egyptian Premier League campaign, is nursing a back injury.
The Cairo giants are seeking to win their 14th domestic double in history.