Scotland striker James McFadden is keen to leave Birmingham following their relegation to the Championship, according to his agent.
With Celtic interested, McFadden could move back to Scotland, while Middlesbrough, West Ham and Aston Villa are also thought to be interested.
Agent Willie McKay said: "James has told me that he wants to leave.
"He is happy when Alex McLeish gave him an opportunity to play first-team football every week but it's a short career and he wants to play at the highest level."
However, Blues manager Alex McLeish is keen to keep hold of the former Motherwell star and said: "We want to keep hold of our best players and James is absolutely vital to our plans."
McFadden, 25, signed a three-and-a-half-year contract when he arrived at Birmingham and has scored four goals in 12 games.
