Amid fresh reports of a rift between manager Jorge Sampaoli and his squad, the Albiceleste are facing a group-stage exit in Russia after collecting just one point from their opening two games.
Messi, who celebrated his 31st birthday over the weekend, is yet to score or provide an assist at the showpiece event, while he had a penalty saved during a 1-1 draw with Iceland.
Mascherano, whose team must beat Nigeria on Tuesday to have any chance of reaching the last 16, said the star forward was only human.
"Leo is fine," he said. "But as a collective, where things don't go as we'd like, we all have our own frustrations.
"He's human and he has his own frustrations but he's desperate to turn the situation around.
"He wants to show the world a different image to the one we've shown in the first two games."
Even a win may not be enough for Argentina, which is bottom of the group – behind Croatia (six points), Nigeria (three) and Iceland (one).