ESPN reported last month that Messi would leave PSG when his contract expires this summer, with the forward considering a move to Saudi Arabian side Al Hilal, the city rivals of Cristiano Ronaldo's Al Nassr.
Galter told a news conference ahead of PSG's final Ligue 1 match of the season against Clermont Foot: "I had the privilege of coaching the best player in the history of football. This will be his last match at the Parc des Princes, and I hope that he will receive the warmest of welcomes.
"This year, he has been an important part of the team, always available. I don't think any of the comments or criticisms are justified. He's always been there for the team. It's been a great privilege to accompany him throughout the season."
Messi has contributed with 21 goals and 20 assists for PSG in all competitions this season.
Messi joined the French champions in 2021 after his 21-year association with Barca ended because of the club's financial issues.
Alongside Kylian Mbappe and Neymar, he helped PSG to win Ligue 1 titles in both seasons he spent in the French capital. However, back-to-back round-of-16 exits from the Champions League meant the club's search for a first European title continues.
He scored 32 goals in 74 games in all competitions for PSG, as well as recording 35 assists.
He was then named men's footballer of the year at The Best FIFA Football Awards in February -- his second time winning the award, adding to his record seven Ballon d'Or trophies.