Dani Ceballos will miss Arsenal's trip to Leicester City in the Premier League on Saturday, the club have confirmed.
The midfielder suffered a hamstring injury against Vitoria SC in Wednesday's Europa League draw, although coach Unai Emery was optimistic it was only a "small" issue.
The problem will keep Ceballos out against Leicester, but Arsenal will continue to assess his fitness.
Ceballos has also been left out of the Spain squad for the upcoming international break which follows the Leicester match.
Emery will have a decision to make in the centre of midfield, with Ceballos' absence potentially opening the door for Granit Xhaka's return.
Xhaka has not played since his angry confrontation with supporters when he was substituted against Crystal Palace last month, the Gunners having seen a 2-0 lead wiped out at Emirates Stadium.
The Switzerland international subsequently explained his actions, citing death threats made against his family on social media, but was later stripped of the Arsenal captaincy.