As many as three weeks have passed since Joao Felix picked up an injury during Atletico Madrid's 0-0 draw against Valencia and Los Rojiblancos have struggled to recover their form since.
Although the extent of his injury wasn't as bad as the medical staff initially thought, the Portuguese starlet has missed five crucial games in LaLiga Santander and the Champions League.
In his absence, Atletico have registered two home wins against Bayer Leverkusen and Athletic Club, while drawing against Alaves and Sevilla, before losing to the German side away from the Estadio Wanda Metropolitano.
However, Diego Simeone's men are just one point behind league leaders Barcelona and Real Madrid and they sit second in their Champions League group, four points ahead of Lokomotiv Moscow and Bayer Leverkusen.
In the five games they have played without Joao Felix they have scored just six goals, with Alvaro Morata and Saul Niguez being the only players who have found the net in his absence.
Diego Costa, Thomas Lemar and Angel Correa have struggled in front of goal, while the last two were those who were entrusted to cover for the Portuguese.
Sunday's game against Espanyol will be the sixth in a row without the 19-year-old, who managed to score three times before his injury.