Stefan Savic has suffered a setback as he bids to return from a hamstring injury.
The Atletico Madrid centre-back has been out of action since Montenegro's 0-0 draw against Bulgaria in Euro 2020 qualifying on October 11.
Atleti announced Savic, who was substituted after 39 minutes of that match, had suffered a hamstring issue but did not offer an estimated recovery time.
And the club revealed in an update on Wednesday the defender has "suffered a relapse of the grade II injury".
Savic has undergone tests and, according to Atleti's short statement, "is pending response to treatment".