Frank Lampard has been sacked by Chelsea after just 18 months as head coach and will be replaced by Thomas Tuchel.
In a statement, Chelsea said "results and performances have not met the club's expectations, leaving the club mid-table without any clear path to sustained improvement".
Tuchel, who left PSG in December and previously managed Borussia Dortmund, will be Chelsea's next head coach and plans are under way to appoint him before the game against Wolves on Wednesday. The German is the only candidate for the role.
Lampard, who is the club's all-time leading goalscorer, enjoyed a good first season as Blues boss, taking them to the FA Cup final and securing qualification for the Champions League.
But after being given more than £200m to spend on new players in the summer, Chelsea find themselves ninth in the Premier League after 19 games, 11 points behind leaders Manchester United and five points off Liverpool in fourth.
Lampard took the side on a 17-game unbeaten run but away defeats to Everton, Wolves, Arsenal and Leicester and a 3-1 home defeat to Manchester City have cost him his job.
In a statement, Abramovich said: "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.
"He is a man of great integrity and has the highest of work ethics. However, under current circumstances we believe it is best to change managers.
"On behalf of everyone at the club, the board and personally, I would like to thank Frank for his work as head coach and wish him every success in the future. He is an important icon of this great club and his status here remains undiminished. He will always be warmly welcomed back at Stamford Bridge."
Tuchel won the DFB-Pokal in 2017 with Dortmund before a brief but trophy-laden spell in Paris which saw him win two Ligue 1 titles and a French Cup, as well as reaching the final of last season's Champions League, which they lost to Bayern Munich.
Analysis: Chelsea lose patience with the Lampard project
Pete Smith:
Those losses to Manchester City and Leicester mean Chelsea haven't won any of the six games they've had against teams currently above them in the table. It's a statistic that does not reflect well on a head coach who is aiming to win respect for his tactical ability.
Nor did the constant team changes over recent weeks, which saw Antonio Rudiger swiftly promoted from exile to first-choice centre back, Jorginho suddenly return to midfield - and Lampard use no fewer than 17 combinations in the front three across the Premier League and Champions League.
The goals conceded column, set-piece susceptibility, and wasteful finishing continued to hold the team back, despite the expensive outlay, and Lampard leaves the team ninth in the Premier League on 29 points. That's five places and three points worse off than at the same point last season.
The rise and fall of Frank Lampard as Chelsea boss - Read the feature in full
Source: m.allfootballapp.com