Gunter is currently on loan at Hellas Verona and he has done well with them. The 25-year-old is very good in the air and Newcastle could use a dominating presence like him at the back.
Fernandez will be out of a contract at the end of next season and Gunter can adapt to the English conditions till then. The German will be ready to take over as a starter from 2021.
Gunter needs a challenge at this stage of his career and a step-up right now would be ideal.