Barca's hopes of retaining their league crown have been fading in recent weeks as they trail leaders Real Madrid by eight points.
Xavi said now is the time for his team to rebound despite getting little rest after Wednesday's 1-1 draw at Napoli in the Champions League last-16 tie.
The Catalan side could provisionally climb to second place with a win on Saturday, moving one point clear of surprise package Girona, who host Rayo Vallecano on Monday.
"It would have been better to schedule the match on Sunday or Monday. But we're playing at that time, and there's no excuse. We will fight and try to win," Xavi told reporters.
"Until we mathematically can, we will fight. We're the ones who can't fail, especially at home. We're not giving up on the league, even though we know it's complicated."
The former Barcelona captain said his team's form has improved since he announced last month that he would step down as manager at the end of the season, which he feels was the right decision.
"I think the decision (to leave) was necessary. The club and the team need a change," the Spaniard said.
"I can see the team has improved, the players have made a step forward, we are more competitive. It was the right decision."
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