The Brazil international - William Saliba's first-choice partner at the back and a member of the 2023-24 PFA Team of the Year - sustained the issue in last weekend's 2-2 Premier League draw with Liverpool.
Mikel Arteta is confident that Gabriel's problem is not serious, but it was enough to keep him out of Wednesday's 3-0 EFL Cup last-16 win over Preston North End, and he remains a huge doubt for Saturday's trip to Newcastle United.
Arsenal were already missing Saliba for the clash with Liverpool due to suspension, while Riccardo Calafiori (knee), Kieran Tierney (hamstring) and Takehiro Tomiyasu (knee) watched on from the sidelines.
Jurrien Timber also left the field due to cramp in the latter stages of that game, after which Arteta's makeshift backline consisted of Thomas Partey, Ben White, Jakub Kiwior and Myles Lewis-Skelly, who could not prevent Mohamed Salah from levelling the tie.
Arsenal transfer team "working overtime" to sign new centre-back
Now, former Manchester United scout Mick Brown has told Football Insider that Arsenal are sure to be pursuing a new defender during the winter transfer window, and sporting director Edu is already scouring the market.
"They're definitely going to enter the transfer market. After Gabriel's injury, the transfer team will be working overtime. They've already been looking at options to help the depth in that position," Brown told the publication.
"Saliba and Gabriel are so important to their team in that defensive unit and you need to know the level won't drop if either of them are out. The defence is the reason Arsenal have become such a force.
"Finding new options for those positions is an issue that will be swamping them at the moment. The back four that ended the game against Liverpool is never going to be good enough to challenge for the title, so they'll definitely be looking to improve that depth."
Gabriel already has two goals to show from nine Premier League appearances this season, heading in Bukayo Saka corners against Manchester City and Tottenham Hotspur to take his tally for the Gunners to 17 efforts in all competitions since 2020.
Do Arsenal need to pursue a new centre-back in January?
It is true that a Partey-White-Kiwior-Skelly backline does not inspire much confidence, as at least two members of that quartet are being played out of their natural position, while the other two are not first-team regulars.
However, that was surely just a one-off emergency from Arteta, whose hand was forced by the issues to all of Gabriel, Timber, Tomiyasu and Tierney, as well as Saliba's rare suspension.
The Gunners boss is seemingly optimistic that Gabriel's issue will heal in the near future, and Calafiori - another left-footed option - should not be out for more than a few weeks either. As injury-prone as Tomiyasu is, he can play anywhere across the backline when fit.
Arteta also has another two unorthodox options to fill in at the back if he is down to the bare bones again; Declan Rice started out as a centre-half, and academy graduate Ayden Heaven made his first-team debut in the Preston victory.
As a result, defence should not be Arsenal's top priority for the January transfer window, as their autumn crisis should not persist into the New Year, but another new midfielder or right-winger would not go amiss.