Chesterfield have sacked manager Dean Saunders.
The former Doncaster Rovers boss only appointed in May, but the club are 16th in the table after Saturday's 4-0 home defeat by Swindon Town.
The Welshman lost 11 of his 20 league games in charge, and the Spireites are only four points above the relegation zone.
The club thanked Saunders for his efforts and added:
Chesterfield have signed Liam O'Neil from West Bromwich Albion for an undisclosed fee.
O,Neil, 22, who can play in defence or midfield, has made five Premier League appearances.
O'Neil made 22 appearances in League One last season while on loan at Scunthorpe United.
The length of the contract signed by O'Neil has not been disclosed.
O'Neil admits that he cannot wait to get started. He said: “ I want to get some experience and develop as a player and I think I’ll be able to do that here. I’m looking forward to it and I’m excited."
Chesterfield have signed experienced Spanish midfielder Angel Martinez.
Known simply as 'Angel', the 29-year-old flew in to watch yesterday's game at Sheffield United and has now agreed a two-year contact.
He was previously with Millwall and Blackpool after starting out at Espanyol in his native country.
Angel's signing comes soon after the capture of Lee Novak who was signed on a season-long loan from Birmingham City and made his debut in Saturday's tw-nil defeat at Sheffield United.
Chesterfield have signed striker Lee Novak from Championship side Birmingham City on a season-long loan.
Spireites manager Dean Saunders is delighted that his patience has paid off:
Novak, 26, joined Birmingham from Huddersfield Town two years ago. He scored 34 goals in 89 league starts for the Terriers and helped them win promotion to the Championship via the play-offs.
Chesterfield manager Dean Saunders hopes he can add to his squad ahead of his debut campaign in charge of the Spireites after the club lost many star players this summer:
Chesterfield are set to unveil their new manager today.
The Spireites have moved quickly after Paul Cook left the club to join Portsmouth yesterday.
The new man in charge will be unveiled at a press conference this afternoon.
Chesterfield have signed Bermuda international striker Rai Simons from non-league Ilkeston Town.
Simons has signed a two-year deal and Spireites manager Paul Cook is delighted to have clinched his signature.
Cook said: "Rai is someone we have tracked for a while. We feel that he will develop as time goes on and have a bright future."
After agreeing a two-year deal at the Proact, Simons said: "I'm excited because I've been looking forward to this moment since moving to England at the age of 15. The set-up sounds brilliant and it is everything I could ask for."
Chesterfield manager Paul Cook has signed a one-year extension to his contract.
Cook, whose previous deal was due to expire in 2016, is now tied to the club until the summer of 2017, together with his assistant, Leam Richardson.
Cook joined the Spireites in October 2012 and has overseen the club's rise from League 2 as champions in 2013/14 and their stabilisation in League 1 during the current campaign.
The contract extension comes in the wake of the January transfer window, which saw the Spireites bring in five new players and sell striker Eoin Doyle to Championship side Cardiff City for a seven-figure fee.
Cook is delighted to commit his future to the club given the volatile nature of football management.