The Brazil international was carried off the pitch on a stretcher during PSG's 4-3 win over Lille on February 19th with what was later confirmed to be an ankle ligament injury.
Galtier added that he plans to fill Neymar's place with a midfielder instead of another attacker, as he did in last week's 3-0 win over rivals Olympique de Marseille, where Lionel Messi and Kylian Mbappe led the team to a second league win in a row.
"Not having him (Neymar) is a big loss, but maybe we can add another midfielder to balance the team," Galtier told a news conference on Friday.
"The work of my two attackers (Messi and Mbappe) and my three midfielders has been remarkable in Marseille. Without Ney we will be with three midfielders and two attackers.
"To tell you that Ney's absence is trivial, no. You have to be one of the best passers in Ligue 1 and it's still a detrimental absence for us."
The reigning Ligue 1 champions, who will also be without defender Achraf Hakimi, look to overturn a 1-0 deficit in the Champions League away at Bayern Munich on Wednesday, but Galtier's priority is Saturday's fixture against Nantes.
"Our squad is weakened by suspensions and injuries, we have to work our way through the league," the French manager said.
"I hope the players don't have the game against Bayern on Wednesday in the back of their minds. It's important to get the third league win in a row."
