Barca's hopes to overtake bitter rivals Real Madrid and this campaign's surprise package Girona in the title race suffered another blow last weekend after a 3-3 home draw against relegation-threatened Granada.
Barca are third in the standings with 51 points from 24 matches, 10 behind leaders Real and five less than Girona, and Xavi is aware that anything other than a win against 17th-placed Celta on Saturday would make matters worse for his team.
"The squad is united and training hard," Xavi told reporters.
"But we can't afford any more slips. I am positive that we can make up the lost ground. That's the direction we are working in, improving in defence, in pressure.
"These are three very important points that would improve our league position."
Barca will visit Italian champions Napoli in the first leg of the Champions League's round of 16 next week, but the Spaniard said his focus remains on the Celta game for now.
"I'm not thinking about Napoli yet. We are totally concentrated on both competitions," he said.
"I think this season could still turn out well. It's all about how the team reacts in the next few games, and we'll be giving everything we've got."
The midfield great, who announced his decision to step down from his position as Barca coach in January, said he wants to finish his stint on the best possible note.
"I love Barca and would give all I have for this season to end on a high note," Xavi said.
When asked about 19-year-old midfielder Gavi, who has been linked with a move to Ligue 1 giants Paris St-Germain, Xavi said the Spanish international is "part of the future" of Barca.
