The 23-year-old, who has three Brazilian caps to his name, is regarded as one of the brightest shot-stoppers in world football.
His representative Paulo Alfonso told Lancenet: "The negotiation for the sale of my client to Napoli is going really well. Talks should be closed soon.
"Rafael is looking forward to going to Napoli. A meeting with Rafael Benitez has been decisive."
Rafael has appeared more than 100 times for Santos.