Arsenal boss Mikel Arteta has confirmed the club have suffered a fresh injury blow with Cristhian Mosquera facing "weeks" on the sidelines with an ankle injury.
The centre-back missed Saturday's 2-1 defeat at Aston Villa with a problem sustained in the midweek win over Brentford.
Mosquera has undergone further tests with the injury considered worse than first feared and Arteta said: "He's going to be out for weeks.
"Unfortunately, it's much more than what we expected, the way he was feeling. So, he's going to be out for weeks."
Matty Cash opened the scoring on 36 minutes before substitute Leandro Trossard equalised nine minutes after half-time.
Trossard was later forced off with Arteta suggesing he may have suffered a recurrence of a calf injury before Emiliano Buendía struck a 95th-minute to spark euphoric scenes at Villa Park.
Arsenal missed the opportunity to briefly open up an eight-point gap at the top of the table and instead saw Villa move within three points before Manchester City play Sunderland later in the day.
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"Every week is going to be like this," Arteta added.
"We are 18 games unbeaten and still the margin is so small. So this is what we have to do.
"We have to focus on ourselves and set standards that today, particularly individually, we didn't raise that level. But the effort was absolutely there. Use that pain to go again. That's football."