United claimed to have ended their interest in 22-year-old Cooper last night with the two sides in stalemate and Chesterfield standing firm over their valuation of the defender.
Leeds have had two bids turned down, the second worth £475,000, and Chesterfield’s board are believed to be holding out a fee of around £1m for the centre-back.
United are unwilling to raise their offer further, saying in a statement: “The club will not be progressing this matter further and any interest in the player has now ended.”
Cooper, who played against Leeds in a friendly at the Proact Stadium last weekend, is understood to be pushing for a move and United’s failure to agree a price with Chesterfield could tempt him to submit a formal transfer request.
The former Hull City centre-back was identified as a potential signing during Saturday’s 2-2 draw between the sides. He was recommended by Nicola Salerno, an advisor of Leeds owner Massimo Cellino.
Cellino has been abroad for most of the past fortnight and was not present at the friendly but United opened negotiations with Chesterfield on the strength of Salerno’s appraisal.
Cooper began his career at Hull and made a handful of appearances for the Humberside club before joining Chesterfield in January 2013.
He was a fixture in the Chesterfield side who won the League Two title last season.