Mikel Arteta confirmed that Arsenal defender Ben White is facing "months" on the sidelines after sustaining a knee injury.
White had been dealing with several issues all season and has missed five games in all competitions for the Gunners already this term.
After struggling through until the November international break, the decision was taken for him to undergo surgery in order to finally address the ongoing problems.
It serves as a bitter blow for Arteta, with only Thomas Parety (13) making more interceptions than White (11) for Arsenal in the Premier League this campaign.
Though Arteta confirmed that the surgery was successful, White is set for a lengthy spell out of the team.
"It has been different kinds of struggles. It has never been the same thing, but we had to make a decision. He has not improved over the last few weeks, unfortunately," said Arteta.
"We know that Ben is going to push every boundary, but it got to the point where we have to protect the player and we decided to do the surgery.
"He agreed with that and it is going to keep him out for a few months."
Asked for a specific time frame, Arteta added: "We have to see how he reacts post-surgery. I don't expect it to be half a year, but I cannot tell you exactly."
It offers a concern for Arteta in the full-back area, with the Spaniard also revealing on Friday that Takehiro Tomiyasu is "going to be out as well for a bit".
There was, however, some positive injury news for the Gunners ahead of welcoming Nottingham Forest to the Emirates on Saturday.
After not featuring for England during the international break, Bukayo Saka and Declan Rice are expected to be fit to feature against Nuno Espirito Santo's side.
Leandro Trossard will also be available for Arteta despite picking up a hamstring injury during the international break with Belgium.
Defender Riccardo Calafiori is also in contention for Saturday's game after a month out with a knee problem.