The midfielder suffered a dislocated shoulder during the 2-1 win over Atletico Madrid, having put his side ahead with a composed finish before landing awkwardly in the aftermath of the goal.
He immediately signalled distress, clutching his shoulder as he left the pitch in clear pain.
Early indications from Mundo Deportivo and Diario Sport suggest Olmo is likely to miss a minimum of three weeks, though Barcelona's medical staff are preparing for the possibility of a longer lay-off.
The concern is heightened by the fact that he previously dislocated the same shoulder during his time at RB Leipzig, an injury that ultimately required surgery.
There are fears he may have suffered a similar setback, which would put his availability for the remainder of the year in serious doubt.
Hansi Flick confirmed after the match that Olmo will undergo a full round of tests to determine the extent of the damage. The Barca manager may now be without another key figure as the fixtures pile up, with the club approaching a demanding run to close out 2025.
Barcelona finish their domestic calendar with La Liga encounters against Real Betis, Osasuna and Villarreal, matches that could prove crucial in the title race.
They also face a significant Champions League test against Eintracht Frankfurt before year end. Losing Olmo for this stretch would be a major blow for Flick as he attempts to navigate a challenging final month of the year.
Hansi Flick has urged Barcelona to maintain their momentum as they travel to Sevilla to face Real Betis today aiming for a fifth straight La Liga win, and the German has used the build-up to highlight the growing influence of Eric Garcia.
Joan Laporta has reignited the tension between Barcelona and Real Madrid after declaring that Los Blancos "represent power", while insisting Barcelona stand for "freedom".
Raphinha has firmly closed the door on any exit from FC Barcelona for the foreseeable future after putting pen to paper on a new deal that keeps him at the club until June 2028.
Marc-Andre ter Stegen's future at Barcelona is moving towards a decisive moment, with the veteran goalkeeper increasingly expected to leave in the January window as he faces a fierce battle to regain his starting role.
