Diego Godin has suffered an injury to his right hamstring, Atletico Madrid have confirmed.
The Uruguay international was taken off early in the first half of the 1-0 win over Athletic Bilbao this week and has subsequently undergone medical tests.
"Diego Godin has suffered a muscle injury of grade I-II in the femoral biceps of the back of his right thigh," the club said on Friday.
The centre-back is expected to sit out Saturday's Liga meeting with Malaga and is a doubt to face Bayern Munich in the first leg of the Champions League semi-finals next week.
Head coach Diego Simeone admits Atleti will miss Godin's presence but is confident that Jose Gimenez, who is almost fully fit after an Achilles problem, can step into the breach.
"We lose authority without Godin, but we have footballers who are doing things very well," he said. "We have Gimenez with us again."