Xavi wants Ousmane Dembele to stay at Barcelona amid rumours of interest from Newcastle United.
The Premier League side, bankrolled after their takeover by a Saudi Arabia-led consortium, are expected to spend heavily during the January transfer window.
Barca winger Dembele is said to be a target, with a report in Sport on Friday suggesting the player's agent, Moussa Sissoko, is prepared to listen to offers as he is not happy with the Catalans' new contract offer.
The France international, a €105million signing from Borussia Dortmund in 2017, has made only two Champions League appearances this season due to injury problems but is in the squad for Saturday's LaLiga game at Villarreal.
Dembele's time in Spain has been blighted by fitness problems, but he remains a dangerous player when available. Since his arrival, Dembele has managed 30 goals and 20 assists in 120 games, a total bettered by only four players, while his average of 1.9 chances created per 90 minutes is second only to Lionel Messi in that time among players to make more than 14 appearances.
Head coach Xavi has made it clear that Dembele is firmly in his plans.
"I had an individual chat with him," Xavi said on Friday. "I made it clear to him how important he was for not only me this season, but for the future.
"It depends on him. Hopefully, he can renew because he's a player capable of making a difference in the next few years."
Xavi added on rumours suggesting Barca could also cash in on some midfield players: "We need them. They're players who are playing and none of them is for sale at all."
Barca beat Espanyol 1-0 in Xavi's first match in charge before a goalless draw with Benfica in the Champions League this week.
Their first away game under the former midfielder pits them against a side who have failed to win any of their previous 24 league matches with the Blaugrana.
Xavi has been impressed with his players' application but admits taking their chances is a concern, Barca having posted figures of 1.56 and 1.39 expected goals against Espanyol and Benfica without scoring from open play.
"I'm really happy with the team's reaction. We win a lot of duels, we're pressing well. I think in attack we have to be more daring," he said.
"We have players who are very young on the inside and have to dare more. I went through it at that age. There's a goal – I can see it in training.
"In general I'm quite satisfied with what I see on the pitch. We want to subdue the opposition and I think we're succeeding, but we have to score to win games."