According to the reports in the Italian press, the keeper agreed a four year contract with Napoli a few days ago, which will see him earn €2m per season.
'Rai Sport' are now claiming that the Portguese international, who was recently named in his nation's World Cup squad, has travelled to Napoli to have a medical on Tuesday.
The Italian side are looking for someone to replace Pepe Reina, who has already gone to AC Milan on a free. Sporting reportedly want €35m for the 30-year-old, but Napoli are looking to pay a maximum of €18m.