Fiorentina have been offered the former Inter Milan prospect for €12m this week.
Abbondanza was Casadei's junior coach at Cesena and told Radio FirenzeViola: "First of all I want to underline that Cesare has always been a good person since he was a child. I didn't discover him because they brought him to the team, but I was lucky to have had him.
"Now he is having a good career. He knew how to do different things on the pitch, then everyone made him play in the same role but he was versatile, he knew football and he was always very intelligent."
Asked if Casadei is ready to be a first-choice for Fiorentina, Abbondanza said: "I think so, then I have never followed the football of the greats so much. The coach can make Cesare show off his qualities even more: (Raffaele) Palladino has always made his players perform well at Monza, so I think he can do the same with Casadei. The experiences abroad will help Cesare."