Girona, with just one defeat, are level on points with leaders Real Madrid, while last season's champions Barcelona are four points behind the top two in third place.
Speaking to reporters on Saturday, Xavi had no doubts when asked if the Catalan minnows could go on to win LaLiga.
"I have already said that against the odds and surprisingly, they can do it," he said.
"I like them because they're brave, they're not afraid."
Girona's rise to the top of the table has taken many by surprise, but Xavi is not among them, and he was full of praise for Barca's next opponents.
"It's a great game. Girona, surprisingly for many people, are leaders, or co-leaders. But for us it's no surprise.
"They're a dynamic team, with a great coach, a system similar to ours, they want to have the ball, they want to be the protagonists - they put pressure on you.
"I congratulate the coach and the team."
Last season Girona finished 10th but held Barcelona to a scoreless draw at the Camp Nou, and lost 1-0 in the home tie, but this Girona are a different proposition, making it harder to predict how they will approach this game.
"Girona last season at our home put pressure on us, and in Montilivi, they closed down. We'll see tomorrow," Xavi said.
"We have prepared the game with several scenarios. They have more variants and individualities. They've improved a lot from last year."
Barca came through a stiff test last weekend with a 1-0 win over Atletico Madrid and before that, a 2-1 victory against Porto secured their place in the knockout stages of the Champions League, setting them up nicely for Sunday's crunch match.
"We've done very well, in terms of morale and confidence. We had two games that were two finals," Xavi said.
"Tomorrow they are a direct rival with a four-point advantage. Tomorrow we have to prove ourselves again."
Barca's goal against Atletico was scored by Joao Felix, a player on loan from the Madrid club, and Xavi will hope the same doesn't happen to his side in Sunday's game.
Girona have two Barca players on loan, and while Pablo Torre has a clause barring him from facing his parent club, Eric Garcia, a late loan deal, is free to face Barcelona.
"I would put the clause on everybody. I think it's illogical for your own player to play against you," Xavi said.
"He will be extra motivated, as happened with Joao Felix."
