Gundogan says Manchester City have too much quality to be conceding every week.
Shakhtar Donetsk's equaliser on Wednesday was the sixth successive game in all competitions that Pep Guardiola's side have failed to keep a clean sheet, a run that includes two draws and a defeat.
“We didn't do all the things right. We struggled a little bit in some areas and, this is the Champions League, it's a very competitive competiton," he said. "All the teams can play very good football and Shakhtar played quite well. We also let them play, we gave them the spaces to play. That shows that, if we don't reach your best level, even if you are a top team, you are going to struggle in this competton. We need to learn from it.
“When you want to become a top team and fight in all the competitions, you are not allowed to concede goals in every game.
“Obviously with all the injuries we are having, all the changes in the squad, sometimes it's not easy but I think there is enough quality in our team, even with the injuries, to be able to play without conceding a goal."