Sebastian Rudy and Zdravko Kuzmanovic gave the Bundesliga side victory at Ibrox, as Rangers suffered their third straight home European loss.
“I’m disappointed – we weren’t good enough again tonight,” 39-year-old Weir told Sky Sports.
“We didn’t play well enough, didn’t put enough into the game and got what we deserved.
“It’s a hard level to play at and we realise we’ve got to be better.”
Weir featured alongside 17-year-old Danny Wilson in Rangers’ central defence in the game.
“We’ve got to take positives from it,” added Weir.
“Lads are getting good experience, we’ve got to get better and learn from the experience.
“It’s a tough lesson but we’ve got a big game on Saturday morning against Aberdeen.”
