Barcelona announced that Messi has hurt his left hamstring and may not play in Argentina’s upcoming World Cup qualifiers.
But his team-mates kept their spirits up when they were joined on the pitch by a dog during training.
Messi will travel to join the Argentina squad, but his “presence in his country’s World Cup qualifying matches will depend on how the injury develops,” Barcelona said.
The club statement says the medical report confirming the injury was jointly approved by their medical staff and the Argentine football federation.
Barcelona reported the injury a day after Messi played throughout the 1-0 win at Athletic Bilbao in the Spanish league.
Argentina host Uruguay on Thursday and then take on Venezuela next Tuesday, and may have to do so without their talisman, who recently reversed his decision to retire from international football.
It will be their first fixtures under new coach Edgardo Bauza, as they look to consolidate their position in the top four of the South American qualifying zone.
Bauza took charge of the training sessions, which featured Premier League stars Pablo Zabaleta, Marcos Rojo, Nicolas Otamendi, Ramiro Funes Mori and Erik Lamela.
And after the interruption provided by their four-legged friend, which seemed to entertain Juventus striker Paulo Dybala rather more than an unimpressed-looking Zabaleta, the new coach was able to drill his players ahead of the crucial qualifiers.