Messi missed PSG's 2-1 win at Lorient as a precautionary measure after suffering from inflammation in his Achilles tendon last week, but Galtier maintained the seven-time Ballon d'Or winner was likely to return before the tournament in Qatar.
Just 11 days before Argentina begins its Group C campaign against Saudi Arabia, Messi has handed the Albiceleste a boost by joining France's Presnel Kimpembe in returning to PSG training.
While Galtier reiterated his desire to treat the concerns of his players seriously ahead of the FIFA World Cup, he is not planning to use Monday's (AEDT) match as an opportunity to make changes.
"All the players are available except Fabian Ruiz," Galtier said. "No player came to tell me that he did not want to play or that he was afraid of making this last match.
"My door is always open. They know they can come and talk all the time. I wouldn't be surprised if a player came to see me and told me that he was apprehensive about the last game.
"I have an obligation to put up a very competitive team against Auxerre. If there is strong restraint, I will be attentive to the comments of my players."
Senegal and Bayern Munich attacker Sadio Mane became the latest big name to suffer an injury scare on the eve of the tournament this week, but Galtier is confident in his medical team's ability to manage players' fitness levels.
"When I see an injured player like Sadio Mane, I'm always sad for him," Galtier added. "The relationship is very direct between my medical staff and the medical staff of the national teams.
"All the doctors of the teams are informed of the state of our players. Our selected players will be operational for Sunday's match. The most important thing is to train well.
"These players who are going to the [FIFA] World Cup are very high-level athletes and competitors. There may be this fear, but it is more around the environment of the players than from themselves."