Diego Simeone’s side are set to face La Liga leaders Real Madrid at the Santiago Bernabeu on Saturday and now look set to be missing one of their key players.
“João Félix suffered a muscular injury in the right leg in the match against the Leganés,” read an Atleti statement.
“Before the persistence of discomfort after the day of rest, the medical services have performed tests detecting the injury and remaining pending evolution.”
Diego Simeone is under pressure at Atletico Madrid following a series of disappointing results - they have slipped to fifth in La Liga and are out of the Copa del Rey.
They suffered a shock loss at third tier Cultural Leonesa in the cup and lost at Eibar in the league, comprehensively, and were second best at home to lowly Leganes in their recent scoreless draw, where Felix picked up this injury.