Joe is a free agent as his contract has expired but if he did move to the Premier League a compensation fee would be negotiated that could bring a seven figure fee into the club. A transfer to Scotland or elsewhere would see Joe walk away and the club getting nothing but memories.
Of course City are trying to keep him and have made a written offer but it would mean a significant increase in salary and that would affect the negotiations due to take place with other City players like Jay Bothroyd and Peter Whittingham who are entering their final year.