Chesterfield have confirmed manager Paul Cook has been released from his contract to join Portsmouth.
Assistant Leam Richardson has also left the club and is expected to join Cook at Fratton Park.
Cook said: “I’d like to place on record my thanks to Chris, chairman Dave Allen and the rest of the board for giving me the opportunity to manage such a great club.
“I’d like to thank the staff in all departments of the club for everything they have done during my time at the club. Most importantly, I’d also like to thank the players, who have been fantastic, both on and off the pitch.
“Finally, thanks to the fans for their superb support.”
Cook joined Chesterfield from Accrington Stanley in October 2012 and guided them to the League Two title in 2014 and the League One play-offs this season.
Richardson added: “I echo the manager’s sentiments and would like to thank everyone at the club, from the chairman and chief executive down, together with all the players, past and present.
“Thanks also to the fans for their tremendous support.”
Chesterfield chief executive Chris Turner thanked them for the fine job they’ve done at the club and wished them well for the future.
“I could not have wished for a better working relationship than the one I have enjoyed with Paul over the last two-and-a-half-years and there is nobody more disappointed than me to see him leave,” said Turner.
“We will be looking to appoint Paul’s successor as soon as possible and the incoming manager will be in the enviable position of inheriting a strong squad.”