The veteran sweeper was on the road to recovery from a serious knee injury last month but he suffered a huge setback after damaging cruciate ligament in his right knee.
Although he faces a lengthy spell on the sidelines, Al-Nahhas was named in the Red Devils' Champions League roster.
Ahli coach Manuel Jose may have the 32-year-old available at his disposal during the competition's group stage if the title holders progress beyond the preliminaries.
There was no room for Anis Boujelbene, who seems unlikely to extend his contract that expires at the end of the season.
Recent reports suggested the Tunisian midfielder might leave Ahli before the closure of the January transfer window.
Midfielder Hassan Mostafa, who used to be a key player in the Cairo giants' squad before falling out of favor with Jose, was left out.
Ahli marketing director Adli Al-Qaeyi recently revealed that Sudanese club Merreikh were interested in acquiring Mostafa's services.
Defender Rami Adel, whose days at Ahli appear to be numbered after a dispute with Jose, was also overlooked.
Ahli squad:
Goalkeepers: Amir Abdul-Hamid, Ramzi Saleh, Ahmed Abdul-Monem
Defenders: Wael Gomaa, Mohamed Samir, Shadi Mohamed, Emad Al-Nahhas, Ahmed Al-Sayed, Ahmed Sedik, Sayed Moawad, Ahmed Ali, Gilberto
Midfielders: Mohamed Abou-Treika, Mohamed Barakat, Hussein Yasser, Ahmed Hassan, Hussein Ali, Ahmed Fathi, Hossam Ashour, Moataz Eno
Strikers: Flavio Amado, Ahmed Hassan Farag, Hani Al-Egeizi, Osama Hosni, Ahmed Belal