Speaking to Tuttomercatoweb, Castagnini said the evidence came during the first half against Juventus, when Frosinone matched their opponents and confirmed his belief that the club can compete at the highest level.
“With Juve in the first half I said that we belong in this division. It gave me that feeling. Even though those of us who work there are convinced of it anyway because of the work we have done.”
Castagnini also remains firmly behind coach Massimiliano Alvini's attacking approach, despite the spaces it can leave at the back.
“Last year we started a journey and lost only three games in a year. It is a style where you leave spaces, attacking aggressively, but it is a game that pays. Why not continue with it?”
He added: “For me, Frosinone must be this, always playing to win the games. It is what Alvini wants, and the players are used to it. You cannot change systems from one day to the next.”
One player to have particularly impressed him is Kvernadze, whose development Castagnini said did not surprise him.
“I knew. I told the president. But many players are doing better now than they did in Serie B. You play more difficult and physical football, but there are also more spaces.”
Raimondo’s arrival, meanwhile, has exceeded even Castagnini’s expectations.
“Exceptional. I did not expect such an impact. But there is still a lot to climb.”
The sporting director was also encouraged by Frosinone’s performance against Como, a side he considers capable of challenging near the top of the table.
“Como are strong, with strong players and a good coach. For me they are a top two or three team. We played a good game, at times we were also fortunate, but we competed with humility. That repaid us and gives us courage. We must not make calculations.”
Castagnini believes the club’s longer-term ambition is to consolidate itself in Serie A before looking higher. He pointed to investment in the squad and infrastructure, as well as the work of president Maurizio Stirpe.
“The first step is to stay in the division, then we can grow. We will encounter difficulties, we already know that today. We must prepare and be good enough to overcome those moments.”
He also praised Frosinone’s commitment to young players, a philosophy shaped partly by his previous work in Juventus' youth sector.
“I love youth football. I go crazy when one of them makes his debut. It is incredible to give them confidence and see them make their debut. Sometimes you have to be a little crazy to do it, but sometimes madness pays.”