Arsenal face being without goalkeeper Petr Cech for up to a month because of a hamstring injury.
Cech was replaced early in the second half of Saturday's Premier League match against Watford, with Bernd Leno coming on to keep a clean sheet as the Gunners won 2-0.
Arsenal said in an injury update on their official website ahead of the Europa League tie at Qarabag on Thursday that Cech had a "left hamstring injury" and was "expected to return to full training in three to four weeks".
As well as not making the trip to Azerbaijan, the veteran goalkeeper will also definitely miss Sunday's Premier League match at Fulham.
Cech could now face a battle to be fit in time for the home game against Liverpool on November 3.
German Leno arrived from Bayer Leverkusen during the summer, but before Cech's injury had only featured in either the Europa League or Carabao Cup.
Arsenal also confirmed that Ainsley Maitland-Niles was expected back in full training during early October, quicker than initially suggested following a fracture to his left fibula.
Teenage midfielder Emile Smith Rowe has recovered from a hip problem, while defender Dinos Mavropanos should be back in training by the end of the month following his groin injury and Laurent Koscielny has also stepped up his rehabilitation from Achilles surgery.
After losing his first two Premier League matches as new Arsenal head coach, Unai Emery has since guided his side to seven straight wins in all competitions.