Chelsea on Monday sacked head coach Frank Lampard after 18 months incharge.
The 42-year-old leaves with the club ninth in the Premier League table after last week's defeat at Leicester City. London-based club has won only once in previous five outings.
His final game as Chelsea manager was Sunday's 3-1 FA Cup fourth round win against Championship side Luton.
Former mid-fielder was appointed on a three-year contract when he replaced Maurizio Sarri at Stamford Bridge in July 2019.
In a statement, Chelsea said: "This has been a very difficult decision, and not one that the owner and the board have taken lightly.
"We are grateful to Frank for what he has achieved in his time as head coach of the club. However, recent results and performances have not met the club's expectations, leaving the club mid-table without any clear path to sustained improvement.
"There can never be a good time to part ways with a club legend such as Frank, but after lengthy deliberation and consideration it was decided a change is needed now to give the club time to improve performances and results this season."
Owner Roman Abramovich said Lampard's status as an "important icon" of the club "remains undiminished" despite his dismissal.
"This was a very difficult decision for the club, not least because I have an excellent personal relationship with Frank and I have the utmost respect for him," said Abramovich.