Sergio Busquets says he admits responsibility for Deportivo de la Coruna's equaliser against Barcelona on Saturday.
Despite leading by two goals, the Blaugrana eventually ended up drawing 2-2.
Busquets told Barca TV: "In the second half with 2-0 we thought it was almost done.
"We had the bad luck of conceding a goal and then my loss of the ball, which I take full blame for the equaliser.
"We must learn to close out games or when we can try to limit any counter-attacks and have plenty of men behind the ball."
On the upcoming Club World Cup, in Japan, he added: "When we travel and make it to Japan we will compete in the cup with great enthusiasm. It's an important tie and we will try our best."