Nabi was appointed to succeed Didier Gomes at the Sudanese giants after the Frenchman departed for Simba SC and finds himself pitted against the champions of Africa in group A for the CAF Champions League.
Ahead of their clash against the Red Devils at the Cairo International Stadium, the Tunisian proved to be rather vocal about Mosimane's side when speaking on Match of the Day via Sada Al-Balad.
"I was waiting for a better performance from Al Ahly in the FIFA World Cup, but the coach has the right to choose the method he deems best suited to Al Ahly," the former Ismaily coach said.
"As a follower of Egypt and the Egyptian clubs, the football level presented by the great Al Ahly is not the same with him."
While Nabi hinted at a lack of attacking threat in the competition he went on to suggest that Mosimane can have no complaints about injuries and fatigue with his star-studded squad.
"The big teams are not affected by absences, and Al Ahly are giants. Mosimane has many solutions, and he has no justifications [for this game] despite fatigue and injuries.
"I was not in the World Club Championship like Al Ahly, but I have more than half of the team who are not present with me due to the conditions of injuries and suspensions."
The Egyptian Premier League champions kick off their clash against the Sudanese powerhouse at 21h00 (GMT+2) this evening.