The Red Devils open their campaign against Gunners away from home in the first leg of the competition's round of 32 on March 20.

They will have to do without Egypt skipper Hassan, who has failed to shine since helping the Pharaohs win an unprecedented third straight African Cup of Nations title in January.

"I have been suffering from a hamstring problem since the end of the Nations Cup," the veteran midfielder said on Ahli's official website.

"I should have rested after the tournament but I opted to play in Ahli's league games."

Hassan, who played a pivotal role in the Cairo giants' league triumph last season after joining as a free agent in the summer of 2008, has already been ruled out of Monday's league game at Asyut Petroleum.

"I told coach Hossam Al-Badri that I'm very exhausted. It's the suitable time for me now to have some rest," the former Anderlecht man added.

"I will return to training once Ahli return from Zimbabwe."

Hassan, 35, is Ahli's top scorer this season with seven goals, two ahead of striker Emad Meteb.