Pablo Mari has been ruled out for the rest of the season with an ankle injury sustained against Manchester City.
The Arsenal defender was forced off in the first half of his side's 3-0 defeat at the Etihad on Wednesday night.
The Spanish defender, on loan from Flamengo, has suffered serious ligament damage to his ankle.
The 26-year-old may need surgery before he is back to full fitness.
Meanwhile, Granit Xhaka is also out of action with an ankle injury sustained in the same match.
The Swiss midfielder's injury isn't believed to be as serious though, and he may be back before the season concludes.
"They are getting assessed at the moment then we will know something more tomorrow morning," Arteta said after the match. "Pablo's one didn't look very good to be fair."
Arsenal's first match back since the coronavirus pandemic brought football to a standstill was one to forget.
The Gunners were well-beaten by the champions, with David Luiz putting in a woeful display after coming off the bench to replace Mari.
The Brazilian was at fault for two goals and got himself red carded in the process.
After the match, Luiz said: "It was not the team's fault it was my fault. The coach is amazing, all the players did amazing, it was just my fault.
"I should have taken a different decision in the last two months. I didn't - it was all about my contract.
"Different decision to try and decide my future as early as possible but I didn't. I don't want to use that as an excuse, it was my fault and that is it.
"I love to be here that is why I continue to train hard and that is why I came today. Nobody asked me to speak, it is up to me to show my face. I want to stay. The coach knows and wants me to stay, we are waiting for the decisions."
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