The 22-year-old is no longer able to wear contact lenses and requires surgery to correct the problem.
Mancini revealed the Italian striker will soon go under the knife and consequently is not ready to feature in City's match against QPR this weekend.
"Mario is not ready to return to the pitch yet. He no longer seems to tolerate contact lenses. He's feeling alright now, but the problem can return any time," Mancini told reporters.
The City manager is already without key forward Sergio Aguero for the next couple of weeks after he picked up a knee injury in the opening game of the season.
He had asked Balotelli to step up to the plate during the Argentine's injury layoff, but now the Italian has joined Aguero on the sidelines.
The 47-year-old will therefore have to rely on the combination of Carlos Tevez and Edin Dzeko to lead the line in the absence of Aguero and Balotelli.