Arsenal midfielder Mohamed Elneny will be out for an "extended period" after surgery on a "significant" knee injury.
Arsenal said they hope to have a "more detailed timescale" on Elneny's return once he begins his rehabilitation.
Elneny last played in Arsenal's 3-0 FA Cup third-round win over Oxford on 9 January, when he scored the opening goal.
He has made only eight appearances in all competitions this season, having also been sidelined by a thigh injury.
An Arsenal statement read: "Everyone at the club will offer Mo all the support he needs and work hard with him to return to action as soon as possible.