Kilmarnock have signed Dundee captain Gary Harkins for an undisclosed fee.
Dundee chief executive Harry MacLean said the player's option to move was part of an agreement made when the club went into administration last season.
"While disappointed that we haven't persuaded him to stay we understand his desire to play at as high a level as possible," said MacLean.
Dundee are also losing midfielder Craig Forsyth to Watford, with the player set to undergo a medical.
The Dens Park outfit agreed compensation for Forsyth with the Vicarage Road side but have been active in seeking new players, announcing the capture of strikers Jake Hyde and Steven Milne along with midfielders Ryan Conroy and Ross Chisholm.