"Further to assessments and scans on Sunday and Monday, we can confirm that Mo Elneny has sustained ligament damage to his left ankle," Arsenal said on their website.
Elneny, 25, is hoping to be fit to play for his country in the World Cup in Russia starting in June.
"We are hoping that Mo will available for Arsenal again this season and we are keeping in regular contact with the Egyptian Football Association," Arsenal said.
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Arsenal take on Spain's Atletico Madrid in the first leg of their Europa League semi-final on Thursday.
Arsene Wenger's side are sixth in the Premier League with 57 points from 34 games.
(Reporting by Shrivathsa Sridhar in Bengaluru, editing by Ed Osmond)
