Neto, 25, has reportedly turned down a three-year contract extension with the Florence outfit with his current deal ending next summer, with both Roma and Liverpool touted as potential destinations.
“Neto has been elusive and hence, I hope he does not leave us,” Della Valle told his club’s official website. “I’m not optimistic.
“Knowing the lad there is something that is not quite right.
“I hope I’m mistaken but if it is true (that he will not sign new deal), I would be extremely disappointed.”
Neto joined Fiorentina from Atletico Paranaense back in 2011 and has started in all of the Viola’s 16 Serie A games this season.
Fiorentina sporting director Daniele Prade expects Neto to give a clear indication as to what his future intentions are once the player returns from Brazil.
“We will see what he (Neto) tells us after the holidays,” Prade said. “We are a transparent club and we will announce everything.”
Fiorentina were held to a 1-1 draw by Empoli on Sunday to finish 2014 in eighth place in Serie A.
The Viola, coached by Vincenzo Montella, are also in the Coppa Italia and will take on Tottenham in the last 32 of the Europa League.