Claudio Ranieri has been sacked as Leicester City manager just nine months after leading the club to the greatest triumph in its 133-year history.
The East Midlands side defied the odds to be crowned Premier League champions for the first time last May in a fairytale season.
But the club said its place in the top flight was now “under threat”.
The Foxes have won just five league games and are currently languishing in 17th place with 21 points, one point above the relegation zone.
They have just 13 more games to try to ensure survival in the top tier.
They lost 2-1 to Sevilla in the first leg of their last-16 Champions League tie on Wednesday.
The contrast in fortunes from last season is all the more stark as Ranieri won the FIFA coach of the year award just a few weeks ago.
The club said Ranieri’s status as its most successful manager was “without question”, but that a change of leadership was “painful” but “necessary”.
Leicester’s vice-chairman Aiyawatt Srivaddhanaprabha said: “This has been the most difficult decision we have had to make in nearly seven years since King Power took ownership of Leicester City.
“But we are duty-bound to put the club’s long-term interests above all sense of personal sentiment, no matter how strong that might be.”
He paid tribute to Ranieri, highlighting his “skillful management, powers of motivation and measured approach”, adding: “We will forever be grateful to him for what he has helped us to achieve.”
Mr Srivaddhanaprabha went on: “It was never our expectation that the extraordinary feats of last season should be replicated this season.
“Indeed, survival in the Premier League was our first and only target at the start of the campaign.
“But we are now faced with a fight to reach that objective and feel a change is necessary to maximise the opportunity presented by the final 13 games.”