Barcelona defender Ronald Araujo suffered a thigh-muscle tear while on international duty, his club said on Saturday, while confirming Jules Kounde also had a thigh issue.
Araujo was taken off inside the first minute of Uruguay's 1-0 loss to Iran in a friendly on Friday night. Kounde lasted just 23 minutes of France's 2-0 Nations League win over Austria on Thursday.
The central defenders will miss their countries' next match and are likely to be unavailable for Barcelona's first games when club football resumes.
With the Clasico approaching on October 16, Barcelona coach Xavi Hernandez may need to construct a new defence for upcoming fixtures, including a reprieve for Gerard Pique, who has been largely frozen out.
Since he was registered to play for the Catalan side, following his summer switch from Sevilla, Kounde has become a key part of Barcelona's rearguard, often used at right-back. Spanish reports suggest he will be out for at least three weeks, although the club did not specify a recovery time.
The international break has been problematic for Barca. Memphis Depay suffered a hamstring injury with the Netherlands in their 2-0 win over Poland on Thursday. Frenkie de Jong was substituted for precaution in the same match.