After De Gea signed a new contract to extend his stay at United until 2023 last summer, Alvarez surprisingly departed a few months later, leaving in September 2019, shortly after Richard Hartis had returned to the club as a goalkeeping coach.
"After almost three years with lots of work and meetings with United to renew him and to make him the best paid player in the world, I learned that he had renewed behind my back," Alvarez told AS of De Gea's new deal.
"Honestly, it felt like a lack of loyalty. During negotiations, he also had a falling out with the person (Jorge Mendes) who had carried out all the talks in order for him to be paid what he was paid. And at the last minute, someone else meddled. I insisted that I didn't like that because it seemed disloyal.
"I asked David why he didn't say anything to me and he said that he was told not to say anything to anybody. This had an impact on me. The way I understand my profession is that you can't help someone develop if you do not have total confidence with them and that's why I decided to leave United."
Alvarez claims United offered him a new deal shortly after they'd confirmed De Gea's extension, but his mind was made up that he wanted to sever ties with the club and the goalkeeper.
"I told them I was going but not because I wanted to leave United. I wanted to stop coaching De Gea," he said. "Aside from being his mentor at Atletico Madrid, where I backed him strongly, I was the person who convinced him to sign for United. I was his right-hand man in Manchester. I came to United thanks to the great work of Jorge Mendes and because Mourinho wanted to sign me to help David develop and to keep him at the club. At that moment, he wanted to leave United."