Chelsea manager Roberto Di Matteo has been sacked after the European champions were left facing elimination at the group stage of the Champions League, the club said on Wednesday.
"Chelsea Football Club has parted company this morning with Manager Roberto Di Matteo," a statement said, following Tuesday's 3-0 defeat by Juventus.
Chelsea said the team's "recent performances and results have not been good enough".
"The club faces a difficult task ahead in qualifying for the knockout stages of the UEFA Champions League as well as maintaining a strong challenge for the top of the Premier League while competing in three other cup competitions," they added.
Tuesday's loss in Turin means Chelsea are poised to become the first ever Champions League winners to be knocked out in the group phase the following season.
Even victory at home to Danish side FC Nordsjaelland in their final group match may not be enough, as a draw between Juventus and Shakhtar Donetsk in the other Group D game would take both sides into the last 16.
Di Matteo was only appointed on a permanent basis in June, having led Chelsea to their first ever Champions League title after replacing his sacked predecessor Andre Villas-Boas in March.
Chelsea beat Bayern Munich on penalties in the Champions League final in May, two weeks after defeating Liverpool 2-1 in the FA Cup final.
"The owner and the Board would like to thank Roberto for all he has done for the club since taking over in March," Chelsea added, saying the Italian "will always be welcome at Stamford Bridge".
The statement continued: "The club will be making an announcement shortly regarding a new first team manager."
Di Matteo, 42, is the seventh coach to have been sacked by owner Roman Abramovich since the Russian billionaire bought the club in 2003.
Former Liverpool manager Rafael Benitez was immediately installed as the bookmakers' favourite to succeed Di Matteo on a permanent basis.
Speaking during a coaching seminar in Abu Dhabi, he confirmed his interest in the position, but did not say whether or not he had been approached by Chelsea.
"What I will say is that I am looking for a club that can challenge for trophies, so Chelsea is one of these clubs," he told newspaper The National.
Pep Guardiola, the former Barcelona coach, and ex-Tottenham Hotspur manager Harry Redknapp were also rumoured to be in the running.
Chelsea had made a superb start to the season, but since losing 2-1 at Shakhtar on September 23, their campaign has come off the rails.
They won seven and drew one of their opening eight league games to move four points clear at the Premier League summit but a 3-2 loss at home to Manchester United last month marked the start of a run of four games without a win.
Saturday's 2-1 defeat at West Bromwich Albion, Di Matteo's former club, left Chelsea four points behind leaders Manchester City in third place.
The loss to United was surrounded by controversy, after Chelsea's claim that referee Mark Clattenburg racially abused midfielder John Obi Mikel prompted a Football Association investigation that is yet to conclude.
A former Chelsea player, who scored in two FA Cup final successes, Di Matteo had been trying to revolutionise the club's playing style by introducing a more attacking approach.
Chelsea spent over £80 million ($127 million, 100 million euros) on new players in the close season, notably bringing in Belgian winger Eden Hazard from Lille and Brazilian attacking midfielder Oscar from Internacional.
Although the quality of their football drew praise from pundits in the season's early months, that initial momentum appears to have disappeared.
Di Matteo, who was born in Switzerland but represented Italy at international level, was in only his third senior managerial position.
He started his coaching career with third-tier MK Dons in 2008 before joining West Brom a year later.