Joao Felix appears set to miss Atletico Madrid's derby against Real Madrid after sustaining an unspecified muscle injury to his right leg.
The Portugal forward suffered the setback during Sunday's goalless draw against Leganes and was unable to train on Tuesday or Wednesday.
"Joao Felix suffered a muscle injury to his right leg during Sunday's match against Club Deportivo Leganes," read a club statement.
"Given the ongoing pain after the day of rest, the club's medical services have performed tests to diagnose the injury. He is pending response to treatment."
While no timescale has been put on a recovery, reports in Spain suggest the injury is not serious but he will miss Saturday's trip to the Santiago Bernabeu.
Joao Felix arrived at the Wanda Metropolitano in a €126million deal from Benfica in July.
The 20-year-old has endured mixed fortunes in Spain thus far, scoring twice and providing just one assist in 17 LaLiga appearances.
Atletico are fifth in the table, 10 points adrift of leaders and city rivals Madrid.