The AC Milan forward has been struggling with pain in his lower back and did not take part in full training with the Azzurri today as a precaution.
Castellacci has admitted that Italy will take no chances with Balotelli and Juventus defender Andrea Barzagli as they build towards a World Cup qualifier against the Czech Republic next Friday, with the Confederations Cup to follow a week later.
He told reporters at a press conference earlier today: "Balotelli has back pain and we have no idea how long he'll take to recover, as with this type of problem we have to evaluate it day by day.
"We tested him running, but he felt pain and so we reserved him for physiotherapy. We certainly hope he will recover in time to face the Czech Republic, but we cannot guarantee that. We are working to have him there, but do not want to force the issue.
"Barzagli could take a while, so we'll now have to test him out for a better idea on how long it'll be."