Barcelona have confirmed Lionel Messi did not train with the squad on Friday due to "personal reasons".
The Liga champions completed their final session ahead of the crunch clash with Atletico Madrid on Saturday without their star attacker, though he has not been ruled out of contention for the game at the Vicente Calderon.
Reports in Spain suggest Messi took time off to be with girlfriend Antonella Roccuzzo ahead of the birth of their second child.
Fellow Argentina international Javier Mascherano did return to training, however, following his return from national team duties this week.
Messi scored twice in Argentina's 7-0 win over Bolivia and once more in the 2-2 draw with Mexico.
Barcelona and Atletico head into Saturday's game having both won their opening two matches of the new season.