The promoted club shocked the champions at the Nou Camp 2-1.
“It's obvious that it wasn't our best game. They were much more effective and they won," Busquets explained.
“I think it was an unjust defeat because they haven't done more than us to win, but they have been effective.
“The calendar is the same for all teams. We all now that these things [international breaks] happen, so it's not an excuse. We have a big squad and the manager decides who plays.“