Davide Astori hasn't been announced as a Napoli player just yet, and apparently there's a good reason for that: according to a report, Astori needs to first sever ties with Puma before he signs with Napoli.
Puma has an athlete sponsorship contract with Astori, and as part of that they hold his image use rights. Napoli traditionally try to hold onto their players' image rights themselves, so this has been an issue in the past. It has yet to actually kill a signing, but it's held up a few from time to time, including Manolo Gabbiadini's last winter.
Among other things, the image rights allow Napoli to control how their players are used in off-the-pitch endeavors, such as advertisements and promotional appearances, and to control the money made off such appearances. It may seem cheap and greedy on the surface, but it also allows the club to make sure their players don't have any time commitments that would potentially conflict with the club's best interests.
It's not expected that getting Astori out of his Puma contract will take too much longer, and Napoli are working with his representation to help the process along. They'll be meeting with the athletic clothing company on Monday in order to try to finish clearing things up, and will be able to finalize his contract once that's done.