Gary Caldwell has been sacked as Chesterfield manager.
The former Scotland international, 35, was appointed in January but was unable to save the club from relegation to League Two last season.
And Saturday's 2-1 defeat by Accrington has left the Spireites in the drop zone with just one win in 10 games.
"We find ourselves in a lowly position after providing him with substantial backing in the transfer market," said director Ashley Carson.
"After making a very poor start to the season, we feel now is the time to appoint a new manager to bring about a change in fortunes."
Caldwell had previously managed Wigan before taking over from Danny Wilson at the Proact Stadium.
The Spireites face Luton in their next League Two match on Saturday, 23 September.