Barcelona are worried by Lionel Messi's fitness levels after he missed an Argentina training session on Saturday, Sport have reported.
The 30-year-old sat out his country's 2-0 friendly victory over Italy at the Etihad Stadium on Friday having complained of a problem in his right leg.
Sport claim that Messi's physical state is 'a worry' ahead of Barcelona's busy schedule in the coming weeks.
He could also be absent for Argentina's meeting with Spain at the Wanda Metropolitano on Tuesday night.
"I have been suffering from this hamstring injury for some time," Messi revealed last week. "I always want to play, but the road to the World Cup is still long. We decided to wait for this game [against Italy] to rest but I'm optimistic about playing against Spain."
Messi has, unsurprisingly, attracted much of the attention in Argentina leading up to this summer's World Cup.
“This is going to be his team,” manager Jorge Sampaoli said. “He is the best of all and is in a stage of maturity that can he can carry the team on his shoulders. It is more his team than mine.”
Barcelona's record scorer also earned praise from veteran Italy goalkeeper Gigi Buffon, who gave his verdict on comparisons with Cristiano Ronaldo.
"Messi is more complete, because he starts deeper, has more technical quality and a vision of the game that is worthy more of a trequartista than a finisher," Buffon said.