Lionel Scaloni's side is facing a group-stage exit after being held to a 1-1 draw by Paraguay in Group B.
Messi scored a second-half penalty to cancel out Richard Sanchez's goal in Belo Horizonte, while Argentina needed Franco Armani to save a Derlis Gonzalez spot-kick to preserve its first point of the tournament.
Even a win over Qatar may not be enough for Argentina, but Messi said there was plenty of confidence in his team.
"I see the team convinced that we will win the next match," he said. "We have to keep looking for the team and improve."
Argentina struggled throughout the first half and fell behind to Sanchez's 37th-minute goal, before Messi equalised after a penalty was awarded following a VAR review for handball.
Armani stepped up for Argentina in the 63rd minute, though, diving to his left to push away a Gonzalez penalty.
"The first few minutes we managed the ball well," Messi said. "After the goal, we messed up a bit. In the second half, we went with everything and we got the draw."
Argentina is bottom of the group on one point, behind Colombia (six), Paraguay two) and Qatar (one).