Andre Villas-Boas, 34, has 'parted company' with Chelsea football club after just eight months.
Roberto Di Matteo has been appointed first team coach on an interim basis until the end of the season, with immediate effect.
A statement on Chelsea's website today said: "The board would like to record our gratitude for his work and express our disappointment that the relationship has ended so early.
"Unfortunately the results and performances of the team have not been good enough and were showing no signs of improving at a key time in the season.
"The club is still competing in the latter stages of the Uefa Champions League and the FA Cup, as well as challenging for a top-four spot in the Premier League, and we aim to remain as competitive as possible on all fronts.
"With that in mind we felt our only option was to make a change at this time."
The bullish Portuguese coach had the worst win rate of all the managers under Roman Abramovich's era, and clocked up a winless run of five matches recently.
He has been criticised by Chelsea players for his tactics and man-management, with midfielder Frank Lampard admitting that the relationship with his coach is "not ideal".
Following Saturday's defeat to West Bromwich Albion, the beleaguered boss admitted that his job was at risk.
"Will this result increase pressure on me? You have to agree with it," he said. "We are in the same position, fifth, but we are now three points behind Arsenal. It is a big, big disappointment. Every defeat Chelsea suffers piles more pressure on any manager."
He added: "Am I the right man for the job? Yes. I wouldn't have taken it if I didn't think that."
Following news of AVB's sacking, bookmakers William Hill installed former Liverpool coach Rafa Benitez as favourite to replace him at 5/4.