Arsenal confirmed on Sunday that defender Sokratis Papastathopoulos has been ruled out for a month with an ankle injury picked up in the FA Cup fourth-round defeat to Manchester United on Friday.
The club said he is "expected to return to full training by the end of February," in an update on their official website.
There was better news regarding the fitness of Laurent Koscielny, who was also forced off against the Red Devils with a jaw problem.
The defender will be "reviewed on a daily basis" after suffering "bruising and soft-tissue swelling to face and jaw.