The former Aston Villa centre-forward has established himself as a the Zebrette's prime striker over the past 18 months.
Nani is a fan and admits he's surprised they're yet to field major offers for the player.
He said on Radio Sportivo: "He's a truly strong player. And the thing that surprises me is that very few people have asked me to sign him.
"Others have attracted a lot of attention, but for me, Davis can play for the top five teams, not just in the Italian league but also in Europe.
"He can do everything; he's truly a complete centre-forward who hasn't yet reached the level he deserves, even due to numerous minor injuries.
"Again, I'm personally a little surprised that I haven't been asked to sign him like so many others, but we have no intention of selling him; we want to build on him for the coming seasons."
Nani also stated: "Centre forwards always mature a little later, especially in a league like the Italian one. He hasn't yet expressed his potential, but he's strong.
"Ours is a very compact team, managed well by the coach, without jealousy. We're in a happy place here. Davis is one of the most experienced in this context."