Atletico Madrid have confirmed that Filipe Luis picked up a hamstring injury during Tuesday's Champions League group match with Qarabag FK.
Luis started and finished the 1-1 draw in Madrid, but a statement from Atletico on Thursday revealed that the Brazilian international had suffered a hamstring problem.
An 'elongation on his left leg's hamstring' were the words used in the statement, although the Madrid giants did not give a timeframe for the left-back's return.
Atletico are facing a group-stage Champions League exit for the first time in eight years after dropping two more points against the Azerbaijan champions earlier this week.
Diego Simeone's side have actually only won one of their last eight games in all competitions, although they will travel to Deportivo La Coruna in La Liga on Saturday afternoon protecting an unbeaten league record this season.