Gardner is now being linked with a £5million move to Sunderland.
When asked if he is leaving or staying at Blues, Gardner said: "I don't know. It's a difficult one.
"I'm unsure exactly what is happening behind the scenes and what the board are thinking.
"Where are we going, what are we planning to do? I don't know.
"At the end of the day, like every player, you have to think of your career. Everything is up in the air at the moment."