Barca's shock defeat at Real Valladolid last week means they head to the Bernabeu third in the table and four points adrift of leaders Real, with Atletico Madrid sitting second.
The 1-0 reverse at the Estadio Municipal Jose Zorrilla was the reigning champions' third loss in their last six league matches, a run that has seen coach Gerardo Martino's future questioned in some quarters.
Barca moved into the quarter-finals of the UEFA Champions League with a 4-1 aggregate win over Manchester City on Wednesday, and get back to league action when they host Osasuna on Sunday.
However, Busquets has already set his sights on the trip to the capital seven days after that clash.
"We have come from an adverse outcome that make it tough (to win the league), but we still have to go to the Bernabeu and fight until the end," he told Marca.
"We are four points behind and it seems we cannot fight for the title, but the (game) at the Bernabeu will decide everything.
"If we win we keep fighting, and if we lose the league will be over."
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