Berizzo last month told his players that he was suffering from prostate cancer in the week building up to Sevilla's dramatic 3-3 Champions League draw with Liverpool.
"No offer has arrived for N'Zonzi", Castro said.
The move will see Montella link up with striker Luis Muriel - who became Sevilla's record signing in pre-season - once again, having worked together at Sampdoria.
"N'Zonzi is just another player in the squad", Castro added. "He wasn't playing on account of a technical decision and now he can go back to playing because of a technical decision". There has been no offer for him.
He added: "What we want is to have good players who help us achieve our sporting goals, which is the way it should be". I've only talked to him about my ideas, based on the players we already have. Details on Sevilla FC's new coaching team will be made public shortly.
"He [Maresca] is a historic person at this club", Montella said.
"Maresca? Enzo made history at this club, he has my respect and is respected in Italy too".
"He is helping me a lot because I still do not know Spanish, but I promise that I will learn it, quickly".
Signings: "I've discussed with the board members of my plans for the team and we'll keep discussing this matter. Support is important to have effective communication".