The Scottish giants succumbed to an embarrassing 7-0 Champions League thrashing to the Catalan club at the Nou Camp on Tuesday night.
"Barcelona are the best team in the world, there's no getting away from that. They have the best front three in the world and they will take three, four, five and more off top teams. But seven for us is going to hurt.
"We can't just write a result like this off because of how good Barcelona are. We're in a hard group and if we think like that already then we're not going to score any goals or win any games.
"There will be a reaction against Man City, we need to show that. I hope we bounce back in the group. We know anything can happen at Celtic Park. We've beaten Barcelona and AC Milan there, so here's hoping we can focus on that and try to get three points as quickly as possible.
"We need to start thinking and focus a lot better during the games and work harder as a team on and off the park."