Serbian Kolarov, who has played in just 45 minutes of competitive action for City, is taking longer than expected to recover from ankle ligament damage.
Italy striker Balotelli, meanwhile, has also seen a delay in his recovery from a damaged knee meniscus.
City's medical staff had hoped to have the left-back available after this week's international break, but with the defender only able to run and do limited ball work, they have now targeted the trip to Wolves on October 30 as a return date, according to the Manchester Evening News.
Mancini had expected the 20-year-old Balotelli to be fit for the visit to Arsenal on October 24 but is now due back in three weeks' time.
City are now banking on their £23million man being ready for the clash with West Brom at the Hawthorns on November 7, or the Manchester derby just three days later.