Fernandez joined the Magpies from Swansea on Thursday afternoon, penning an initial two-year deal with the club.
“We were working for one year in Naples and it was really good. I had a great experience, won trophies in Naples, and he was the key to my move to Swansea as well," the 29-year-old told NUFC TV.
“He told me about the Premier League and the club, and it was very important. We found a way to work together, and now him and the staff are working really hard to improve the players and the team, so it's something that is really good for everyone at the club. I'm really excited to work with him again.
“At that time in Naples I was 23 so I learned a lot under Rafa. I had the chance to come to the Premier League, and now he believes in me because he knows what I can do for the club and the team. I like the way they work so I try to show my best for the club."