Arsenal goalkeeper Petr Cech has been ruled out of the north London derby against Tottenham with a hamstring injury sustained in Wednesday's shock loss to Swansea City.
The Gunners suffered a 2-1 defeat at the Emirates Stadium and will now be without Cech against second-placed Spurs on Saturday after he picked up the problem running back towards his own goal after going up for a stoppage-time corner.
David Ospina will come in to replace him for the first time in the Premier League this season.
Defender Laurent Koscielny, who missed the Swansea match with a calf injury, will also be absent for the crucial derby against Spurs.
Boss Arsene Wenger confirmed: "Cech got a muscular problem at the end of the game and he will not play on Saturday. I have full faith in Ospina."