Nathan Cleverly's chances of defending his WBO Cruiserweight title on Saturday, November 10 in Los Angeles have been dealt a severe blow.
Coyne has revealed that King has threatened to sue him if the fight goes ahead as he believes that the fighter is still under contract.
He told World Boxing News: "I personally am 100% ready to go forward with this fight and I can't wait to oppose Nathan Cleverly next month, but Don threatened the WBO and Frank Warren with a lawsuit and that seems to be that.
"It is a dreadful situation that has cost me dearly."
Cleverly will be forced into a non-title bout if Warren cannot get a defence sanctioned by the WBO, who have insisted that he must face a fighter ranked in their top 15.