Arsenal manager Mikel Arteta said Thomas Partey will be sidelined for several weeks with a groin injury.
The 30-year-old missed Sunday's dramatic 3-1 win over Manchester United at Emirates Stadium after sustaining the problem in training on Thursday and will undergo further tests.
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The Ghanian FA had already confirmed Partey would miss this month's Africa Cup of Nations qualifiers against the Central African Republic and Liberia, but Arteta hinted the midfielder could be sidelined for a lengthy period if the club's worst fears are confirmed.
"It doesn't look good," Arteta said. "I believe he'll be out for weeks. I think it's more a groin [than a hamstring problem], but it could be something in between both."
Arteta hailed his side's perseverance after coming from behind to beat United. Marcus Rashford gave Erik ten Hag's team a 27th-minute lead only for Martin Odegaard to equalise 100 seconds later.
After Alejandro Garnacho had an 88th-minute effort ruled out by VAR for offside, Declan Rice scored his first Arsenal goal in the sixth minute of added time before Gabriel Jesus added a last-gasp third.
"We all work so hard to live moments like this," Arteta said. "Those moments are going to stick with us. To see the crowd so connected with the team again and celebrate in a big match, with the history of these clashes it's something great. So I'm really happy.
"A team needs different tools to win matches. It needs the capacity to react as well. I think we did that really well in the first half and it made the difference. I think that set the tone and brought some calmness to the team as well."