London
Chelsea sacked manager Frank Lampard on Monday after 18 months in charge, with former Paris Saint-Germain boss Thomas Tuchel hotly tipped to replace him at Stamford Bridge.
Lampard signed a three-year deal in July 2019, leading Chelsea to the FA Cup final and a fourth-placed Premier League finish in his first season in charge.
Chelsea cruised into the last 16 of the Champions League and briefly topped the Premier League table in December after an impressive start to the season but they have now slumped to ninth after five defeats in eight matches -- 11 points behind leaders Manchester United.
Sunday's 3-1 FA Cup fourth-round win against Championship side Luton was not enough to save the former England midfielder.
The club said it had been a "very difficult decision" to part ways with the 42-year-old, who is their all-time record goalscorer.
"We are grateful to Frank for what he has achieved in his time as head coach of the club," Chelsea said in a statement.
"However, recent results and performances have not met the club’s expectations, leaving the club mid-table without any clear path to sustained improvement."
In a rare public statement, the club's Russian owner Roman 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."
Former PSG boss Tuchel, who was abruptly fired by the French champions in December, is in line to take over, it was widely reported.
Defeat to Arsenal at in the FA Cup final Wembley in August was followed by a 7-1 aggregate defeat to eventual Champions League winners Bayern, convincing the Blues board they needed to splash the cash.
Ben Chilwell and Kai Havertz arrived for big fees following the earlier signings of Hakim Ziyech and Timo Werner but an outlay of around £220 million ($300 million) has failed to translate into improved results.
Lampard's points-per-game average of 1.67 is the lowest for any Chelsea manager since Abramovich arrived at Stamford Bridge in 2003.
"It's not where we want to be," said Lampard. "I am worried. From the form we were in to get so quickly in to the form we're in now... we should be better than losing five in eight."
The former playmaker won three Premier League titles during his glittering playing career at Stamford Bridge, as well as the Champions and Europa Leagues and other domestic honours.
Lampard's first managerial posting was at Championship club Derby. In his one season in charge, they reached the Championship play-off final, where they lost to Aston Villa.
His departure marks the 14th managerial change since Abramovich's takeover, which transformed the London club into English and European heavyweights.
"He is an important icon of this great club and his status here remains undiminished," said the Russian. "He will always be warmly welcomed back at Stamford Bridge."
"Where do you begin?" he tweeted. "Against the odds made top 4 last season and qualified impressively to the knockout stages of the @ChampionsLeague this season. Bought some good players who will settle in given time. Madness."
Tuchel only became available a month ago when he left PSG, less than five months after taking them to the Champions League final, which they lost to Bayern.
The 47-year-old German won back-to-back league titles with PSG, but that was not enough to satisfy the club's Qatari owners, who replaced him with former Tottenham manager Mauricio Pochettino.
Prior to PSG, Tuchel impressed at Borussia Dortmund, having started his managerial career with Augsburg and then Mainz.
