Galtier was unhappy with his side's performance and feels that they cannot blame their display on playing a Europa League qualifier during the week.
"We shouldn't have conceded the penalty and we should have been much more consistent throughout the match," Galtier told reporters. "It's tough to score when you only have six chances in a game.
"Sure, we're coming out of a European match midweek, but you need to be tougher mentally and show character in the long term. We lacked anchor points up front; we need to be more daring. We need to bring in some new players in because in the league, it has been flagrantly obvious that we're not creating as many chances as we did last season. We need a bit more power and quality.
"We should have taken a point home from Lille, but it's not just a question of points. Until new forwards arrive, the lads who are playing need to dig deep and help us be more dangerous. It's about mental strength."
Saint-Etienne host Bordeaux at the weekend after their Europa League qualifying return leg against Esbjerg on Thursday.