Sevilla thumped Barca 4-1 on Sunday, just days after the Catalans lost at home to Champions League opponents PSG.
Gerard said on Movistar +: "It's clear that there's a drop in results at FC Barcelona... What I do see is that the defeat could lead to a rethinking of the defensive aspect.
"It's one thing to push forward and do it well, as he's done on many occasions, and another to be... suicidal...
"Without putting the ball under pressure, teams have to constantly draw their line in the end... (Flick) has been here for a year now, a year and a half, and we have to be critical of this Barça in terms of the way they defend.
"Tere was no intensity in the pressing, nor was there the necessary timing to unbalance Sevilla's players on many occasions."