Brau was close to former Barca captain Lionel Messi during their time together at the club and took issue with Xavi's claims and criticism regarding Blaugrana president Joan Laporta.
The former Barca coach insists Messi was ready to return from PSG after the 2022 World Cup, but was blocked from doing so by Laporta.
Speaking with ABC, Brau has now launched a fresh broadside at the Barca great: "We were incompatible with the people Xavi wanted to bring in; we didn't agree with his way of working and proof of that is that nothing remains of what he brought in.
"You can't destroy club structures on a whim. Everything that has come after is no better, despite a huge financial investment. Nothing remains of that, and it hurt me that it was destroyed by someone who was part of the club."
Brau was the founder of the club's Physiotherapy Department until he left in 2021 following Xavi's appointment.
Asked to compare Messi with Lamine Yamal, Brau also said: "Leo had a very good advantage: he had a supportive environment, someone who protected him to the fullest, Ronaldinho, and he had everything else, including Henry , Eto’o … He had people around him who acted as a shield.
"Lamine doesn’t have anyone like that today. When did Leo become a regular starter? Proof of that is that he’s playing today at 38 and he’s fantastic.”