The Blues keeper is currently on a season long loan deal with Midlands neighbours West Brom but should Blues manage to get promoted back to the Premier League this season he is expected to remain at St Andrews.
"I honestly haven't got a clue," Foster has said.
"As far as it stands it was just a season-loan deal and that was that.
"It just depends on what happens at the end of the season.
"If Birmingham go and get promoted and get back in the Premier League then I will be back there playing football with Birmingham - simple as that.
"If it doesn't happen, then there is a decision to be made on both parties.
"It's out of your hands to a point. I will have to bide my time and wait and see."