David Luiz will miss Arsenal's opening game of the season against Fulham on Saturday after failing to recover from a neck spasm.
Luiz has become a trusted defender for manager Mikel Arteta despite several high profile errors last season.
The Brazilian was expected to start the season at centre-back to allow new arrivals William Saliba and Gabriel Magalhaes time to adjust to the Premier League.
But Saliba and Gabriel could be pressed into action this weekend at Craven Cottage in the absence of Luiz.
Arteta is also without four other defenders with Sokratis, Calum Chambers, Pablo Mari and Shkodran Mustafi all nursing injuries.
Youngster Emile Smith Rowe, who was expected to play a role this season in the first team, injured his shoulder in training this week.
But Arsenal have confirmed he could return to training next week when he has a protective sling removed.
Gabriel Martinelli remains a long-term absentee after undergoing an arthroscopic procedure to repair a lesion in the cartilage of his left knee.
The Brazilian is aiming to return to full training by the end of the year.
Meanwhile, Arsenal have announced Arteta's job title at the club has been changed from head coach to first-team manager.
In recognition of the all-emcompassing work done by Arteta since his arrival in December, the Spaniard has been rewarded by Arsenal with the alteration.
Chief executive Vinai Venkatesham told Arsenal.com: "Mikel's been here since the end of December and the last nine months have probably been the most challenging nine months in Arsenal's history - and we've been around for 134 years. Despite all of those challenges, Mikel has been driving this football club forward.
"He has lifted the spirits and lifted the energy here at London Colney and with Arsenal fans all across the world. He is doing an absolutely phenomenal job.
"The other thing that's clear is that right from the day he walked through the door, he was doing much more than being our head coach. So we're going to be changing his job title going forward. He'll move from head coach to be the first-team manager. That's recognition of what he's been doing from the day he walked in the door, but also where we see his capabilities.
"He is doing a great job of coaching the first team and that's his primary responsibility, but there is so much more that he can bring and that's why we're making this change, in recognition of his capabilities and also the job that he's doing already."
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