The 21-year-old joined the Blues two years ago after signing from Inter Milan, but has spent more time with Reading and Leicester City on loan than in a Chelsea shirt.
Casadei would have hoped for a chance this season, but has now been told by Nunziata to leave and develop away from England.
“Last year Cesare had a good first part with Leicester, then he went to Chelsea and played little,” the Italian U21 boss told Rai Radio 1 Sport.
“This year they kept him there, I advised him to see how it goes until January, otherwise it’s right to look around for another solution.
“The important thing is that the boys play. If they find a team in Italy, even better.
“But the experience abroad is also formative. For example, after playing in Switzerland, I found (Mattia) Zanotti to have improved a lot and grown a lot.”