Barcelona sports director Andoni Zubizarreta admits beating Real Madrid to the title is now a tough task.

Zubizarreta says Barca need to keep the heat on Madrid in case the in-form pacesetters start to falter.

"It's obvious that we don't depend on ourselves, nor on the game against them (Madrid) at the Nou Camp. But we cannot worry about what others are doing," Zubizarreta was quoted as saying in the Spanish media ahead of Barca's Champions League trip to Bayer Leverkusen.

"Mathematically it is difficult, but we need to try.

"We have to continue competing, keep the pressure on in the league because if anything happens to Madrid we need to be there to take advantage. But if Madrid are able to continue picking up points as they have been doing they will win the league."