The 21-year-old, who has been deputising alongside Piero Hincapié in the absence of first-choice pairing William Saliba and Gabriel Magalhães, was visibly struggling moments before the break. After attempting to continue, he signalled to the bench and was promptly replaced by Jurrien Timber. The severity of the issue remains unclear, but his withdrawal marked a worrying escalation for a squad already stretched thin.

Arteta entered the Brentford fixture without Saliba, who missed the 1-1 draw against Chelsea with what the club described as a “bizarre” training-ground knock.

Speaking earlier in the week, the Arsenal boss offered glimmers of optimism, insisting the French defender’s issue should only rule him out for “a matter of days” though he stopped short of offering guarantees. The manager also referenced Saliba’s earlier ankle injury from August, labelling it similarly “random” and “unlucky”, reinforcing the unpredictable nature of the defender’s recent setbacks.

Gabriel’s continued absence only compounds the pressure. The Brazilian has been a near ever-present under Arteta, forming one of the league’s strongest defensive duos with Saliba. Losing both simultaneously has forced Arsenal into an improvised back line and now Mosquera’s potential addition to the injury list leaves Arsenal dangerously short as fixtures pile up.

Timber, returning from long-term injury himself earlier in the campaign, was thrust into action sooner than planned. Though he provided stability, the wider implications are clear: Arteta’s options for rotation are dwindling. With Champions League commitments, league title ambitions, and domestic cup fixtures still ahead, the strain on Arsenal’s defensive resources threatens to become a defining storyline of their season.

Arsenal’s medical department will assess Mosquera in the coming days, but the timing could hardly be worse. The Gunners have already seen midfield anchor Declan Rice forced off recently, while several senior players have battled recurring fitness problems a trend that has frustrated Arteta in recent weeks.

The manager, while maintaining composure publicly, has repeatedly emphasised the importance of squad depth and fitness management. Yet with three central defenders now sidelined, Arsenal faces the prospect of navigating a congested schedule with only one fit senior centre-back.

The club will hope for positive news regarding both Saliba and Mosquera in the coming days, but Wednesday’s setback underscores a deeper concern: Arsenal’s title push may hinge as much on medical updates as match performances.