Messi continued his impressive start to his second season in France with his first goal from a direct free kick for PSG in their 2-1 win over Nice in Ligue 1 on Saturday.
The 35-year-has now scored five times and laid on seven assists for his teammates in nine Ligue 1 matches this season.
The seven-time Ballon D'or winner underwhelmed in his debut season in France, scoring just six times in the Ligue and was not named among the contenders for this year's Ballon D'or.
Messi however looks back to his very best this term ahead of featuring at his fifth World Cup in Qatar later this year.
Galtier believes the former Barcelona forward can go on to take his place as the best player in world football if he continues his fine form for the Parisians.
"I have an incredible pleasure to see him every morning in training," Galtier said in his post-match press conference. "He is playing well and is happy every day when he trains.
"He is a player who has always had a habit of scoring a lot of goals in a season. This year he's regaining a taste for scoring and is becoming decisive for us.
"Whether he can be the best player in the world again, I'd say yes because he's in incredible shape and he's well prepared.
"He has a relationship with his team-mates that makes him happy. When he's happy, he performs; when he performs, he can reach the standards seen throughout his career."