The Italians are interested in 23-year-old Reguilon and have asked Madrid for information about him.
Madrid are open to a sale because they well covered at left-back position with Marcelo and Ferland Mendy vying for minutes.
According to Di Marzio, Napoli were told they would have to pay in the region of €20/25m for Reguilon.
If Napoli firm up their interest, they will try to negotiate a loan with an option to buy.
However, the Partenopei face serious competition from the Premier League for Reguilon.
Reguilon is currently on loan at Sevilla and starts in their Europa League tie with Wolves on Tuesday night.
His performances for Sevilla led to him being voted the best left-back in La Liga for the 2019-20 season.