Balotelli suffered the original injury during his debut against Timisoara in the Europa League in August.
The 20-year-old was forced to have an operation that kept him out for two months.
However, the injury flared up again during his hat-trick performance against Aston Villa on December 28th since when the controversial front-man has been absent from the first team.
The Eastlands medical staff have advised Balotelli to rest for four weeks and then resume training, in the belief that will rectify the problem.
"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."