Arsenal suffered a major blow in the opening minutes of their Premier League clash with title rivals Liverpool on August 31.
Centre-back William Saliba went off after only five minutes due to an apparent injury sustained in the early exchanges. Cristhian Mosquera came off the bench to replace the France international.
The Gunners were already without Bukayo Saka heading into the game at Anfield, while captain Martin Odegaard was only fit enough to be a substitute, so the loss of his most important defender would have caused great concern to manager Mikel Arteta.
The Sporting News looks at the latest news on Saliba's condition.
MORE: Latest updates, highlights from Liverpool vs. Arsenal
What happened to William Saliba vs. Liverpool?
Saliba appeared to land awkwardly after winning an early header against Hugo Ekitike and went down.
The Arsenal bench took action swiftly, with Mosquera quickly readied to come on.
Saliba made no sustained attempt to continue, with the player and his manager immediately convinced a change was necessary.
William Saliba latest injury news, updates
There has not yet been an update on Saliba's condition, although he was at least able to walk off the field.
The promptness of Arsenal's action suggests Saliba could have suffered a significant setback. In a game of such magnitude it would be normal for a key defender to try to continue through a minor injury.
Arteta will no doubt be asked for an update on the 24-year-old's prognosis at his post-match news conference.
Arsenal were already without influential duo Saka and Odegaard from kickoff against Liverpool, although the club captain did make the bench.
Saka is expected to spend a month on the sidelines, but his deputy Noni Madueke started impressively on Merseyside.
In terms of injury cover, Arteta certainly isn't short of alternatives to Saliba. His starting team at Liverpool featured four natural centre-backs. Nevertheless, being without the influential France international for a concerted length of time would feel like a notable blow.
Arsenal injury list lengthens with Saliba blow
Before Saliba went off against Liverpool, Arsenal were already struggling with a number of injury problems.
Bukayo Saka
Saka suffered a hamstring injury in his left leg in the 5-0 win over Leeds United. Arteta said surgery is not required, but the winger is still facing a few weeks out.
Estimated return date: After September international break
Martin Odegaard
Odegaard hurt his shoulder against Leeds but was not seriously injured, and he was able to make the bench against Liverpool.
Kai Havertz
Havertz sustained a knee problem after the opening-weekend win over Manchester United, and it was later confirmed that he would require surgery. The timescale for his return is unclear, but Arteta expects him to be out for a number of weeks.
Estimated return date: Unknown
Ben White
White missed training in the build-up to the Liverpool game with what was reported to be a minor issue. He is not expected to be out for long.
Estimated return date: After September international break
Christan Norgaard
Arteta said the new signing had a "little issue" at the start of the season. He is yet to make a matchday squad in the Premier League this season, and he was left out of the Denmark squad for the September internationals as a precaution.
Gabriel Jesus
Jesus tore his ACL in January and is still recovering. It is hoped that he will be able to play again before the end of the year.
Estimated return date: November