The Portuguese forward, on loan at Barca from Atletico Madrid, failed to convince coach Diego Simeone during four years in the Spanish capital.
Atletico playmaker Antoine Griezmann this week said Felix lacked "consistency" or "got tired" of finding it, while midfielder Saul Niguez also said Felix had plenty to improve on.
Simeone said Saturday he did not want to speak about the forward because he was not at the club, despite still being an Atletico player.
"(The criticism) should be extra motivation against Atletico," Xavi told reporters Saturday.
"I see he is motivated and happy, he is being consistent, I am happy with his performance and how he has adapted to the group."
Barcelona loaned Atletico's record €126 million (£108 million) signing in the summer and after an impressive start, he began to struggle.
Felix scored his first goal in 13 matches against Porto on Tuesday as Barcelona secured qualification to the Champions League last 16.
The victory helped quieten the negative noises around the club after a string of bad performances and Xavi hopes they can build on it against Atletico.
"We have to find our game, the second half against Porto was very good ... we have to be more consistent," said the coach.
"We can't say we're in our best moment of the season, (but) we have had some very good minutes.
"We have to improve our performances and the consequence will be good results."
Xavi confirmed goalkeeper Marc-Andre ter Stegen was still sidelined because of back pain and will not feature at the weekend.
Champions Barcelona are fourth after last weekend's draw at Rayo Vallecano, while Atletico Madrid are third, level with the Catalans on 31 points.
Simeone said his team was still at a disadvantage against the traditional big two - Barcelona and Real Madrid - but were always looking to level the playing field.
"In principle, Barcelona and Madrid start with more chance of winning, but in recent times we've cut the gap," said the coach.
"This is about deeds and not words, and we will keep working to keep cutting into it."
