The 62-year-old, who coached Montella during a short-lived tenure at Roma between 2004 and 2005, said that the former Italy international has proven his potential by guiding Viola to fifth in Serie A.
Del Neri described Fiorentina as an "excellent" team, but also believes that they may be susceptible away from home.
"He was already very alert when he played," said Del Neri. "I got to know him when he perhaps already had in mind that he wanted to become a coach.
"He's very talented and he's proving that. Fiorentina are an excellent side, but perhaps they are less efficient away from home."
Fiorentina have yet to win away from home this season.