Arsenal will be without Henrikh Mkhitaryan for at least six weeks because of an injury to his right foot, the London club said on Monday.
The Armenia playmaker fractured a metatarsal in Wednesday's 2-0 League Cup quarter-final defeat by neighbour Tottenham and was replaced at half-time.
The 29-year-old Mkhitaryan joined Arsenal from Premier League rival Manchester United last January in an exchange deal that saw Chile striker Alexis Sanchez travel in the opposite direction.
Arsenal are fifth in the standings, on the same points as fourth-placed Chelsea, and will visit Brighton for their next league fixture on Wednesday.