Augusto Fernández suffers ACL tear in Atlético's win over Depor
Atleti defender José María Giménez was also on the end of an injury blow in Sunday's LaLiga encounter at the Vicente Calderón.
Augusto hit by torn ACL
Fernández was taken off midway through the first half at the Vicente Calderón having landed awkwardly on his right leg, with Gabi replacing the midfielder.
Following the match, Atlético released a medical report that confirmed the worst fears, announcing that the Argentine has suffered a torn anterior cruciate ligament.
The 30-year-old is set for surgery on Tuesday and, although Atleti have not specified his recovery time, it is thought he will be out of action for around seven months.
Fernández missed six weeks earlier this year due to a ligament injury picked up in his other knee, soon after joining Los Rojiblancos.
Giménez in muscle injury
Atlético have confirmed that the Uruguayan, who was carried off in tears ten minutes before half time, has a "muscle injury in the adductor longus of the right leg" and is to have more tests.
It is initially understood that the 21-year-old faces roughly two to three weeks on the sidelines.