João Félix, 24, joined Barça on a season-long loan from Atlético in the summer and will face his parent club for the first time on Sunday at the Olympic Stadium.
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Atlético forward Antoine Griezmann said this week the Portugal international "lacked the consistency" to succeed at the club, while Saúl Ñiguez noted "he could have done things" better during his four years with the Rojiblancos.
"The comments made by his former teammates should motivate him," Xavi told a news conference on Saturday.
"Playing against your old team is an added motivation. He is motivated, happy and consistent [at Barça]. I am delighted with his performances and how he has adapted to the team.
"I wasn't at Atlético with him. Here we have seen a really happy João Félix, hard working, dynamic, loved in the dressing room and a joker. He works hard for the team and scores important goals. I have no complaints."
João Félix, who ended a 12-game goal drought by scoring the winner against FC Porto on Tuesday, has spoken since joining Barça about how much more comfortable he feels with the Catalan team's style of play.
In an interview with ESPN on Friday, he said that Atlético's players "would be lying" if they claimed they did not want to play more attacking football as well.
Sunday's game promises to be a clash of those two styles, although Atlético have outscored Barça in both LaLiga and the Champions League this season and go into the fixture ahead of them in the table on goal difference.
"It's an important game," Xavi added. "It's still only three points, but it's against a direct rival who are in great form.
"We have to dominate the game, circulate the ball high up the pitch and attack the spaces. They defend in a low block and are aggressive. It will be difficult.
"I would highlight the work done by coach [Diego Simeone]. Every day that passes I have more respect and admiration for him. Their style is different to ours but it's to be praised."
A win for Barça, who booked their place in the Champions League round of 16 in midweek by beating Porto, will see them move back into the top three, ahead of Atlético and behind Girona and Real Madrid.
"If things don't came off [on Sunday], there is still time," Xavi said of the importance of the game in terms of the LaLiga title race.
"But we want to continue the good dynamic. The second half against Porto was very good. It is a test against a top team this weekend, but LaLiga is long. There are four points between the top four, if things don't work [on Sunday], we keep going."