The Egypt international was carried off on a stretcher on the stroke of half-time having fallen awkwardly while competing for the ball with Hammers skipper Mark Noble.
Gunners boss Arsene Wenger said after the 4-1 win that the injury
didn't look good". But the club feel Elneny, 25, could make a return this season and feature in Egypt's World Cup campaign.
"Further to assessments and scans on Sunday and Monday, we can confirm that Mo Elneny has sustained ligament damage to his left ankle," read a statement on the official Arsenal website.
"We are hoping that Mo will be available for Arsenal again this season and we are keeping in regular contact with the Egyptian Football Association.
"The midfielder was injured just before half-time during Sunday's 4-1 home victory over West Ham United. Further updates will be made in due course
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