Gardner, who is City's leading scorer with four goals this season, missed Saturday's shock 1-0 home success over Chelsea with an ankle injury.
Blues boss Alex McLeish, who is guarded about Gardner's chances of being fit to face Villa on December 1st at St. Andrews, said: "We are still awaiting the results coming from the specialist in London.
"We are hopeful Craig is only going to be out for two to three weeks so we will await the specialist report."
He added: "We thought it (the ankle) might be worse than it actually is.
"Is he out of the derby? I don't know, I need to check with the doctor."
Gardner moved across the city to Birmingham in January and helped the club he supported as a boy to a goalless draw at Villa Park last month.
His replacement, Lee Bowyer, scored the winner against Chelsea - his first goal for 11 months.