City medical staff have advised Balotelli to rest for four weeks and then resume training, in the belief that will rectify the problem.
However, Mancini is not happy at the situation.
"It is bad news," admitted the City chief.
"I am worried because he can't play for another three or four weeks at an important moment for us.
"To have an operation done and then to have another problem two months later is strange.
"He may need surgery. We just don't know. He must rest, then he will have treatment and work. Hopefully then he will be OK."