Ranieri's side were beaten only three times last season on their way to lifting the trophy but the loss at the Stadium of Light was already their seventh of the current campaign.
Leicester's title defence is now the worst in Premier League history and they sit just two points above the relegation zone.
Could the Foxes become the first champions since Manchester City in 1938 to be relegated the following season?
Here, Press Association Sport takes a look at some of the areas where it has gone wrong for Leicester.
KEY PLAYERS OUT OF FORM
Jamie Vardy and Riyad Mahrez set the Premier League alight last season, scoring 41 goals between them, but both players are a shadow of the ones they were just a few months ago
Twelve months ago Vardy had just set a new Premier League record for scoring in 11 consecutive matches
Now, the striker is currently without a goal in 16 outings in all competitions for the Foxes
Mahrez has netted seven times this season but looks completely out of sorts
Nothing is coming off for him and his confidence looks shaken
CONTRACTS = COMFORT ZONE?
Could an explanation for Leicester's dramatic drop in performance be the fact that several members of the squad signed lucrative new contracts over the summer? Last season Leicester's players were hungry and eager to impress - perhaps even to put themselves in the shop window
Vardy and Mahrez could have moved to other clubs in the close season but opted to remain at the King Power Stadium and along with Wes Morgan, Kasper Schmeichel, Christian Fuchs, Andy King, Danny Drinkwater and Danny Simpson put pen to paper on new deals
With their futures secured, have they taken their foot off the gas?
The loss of N'Golo Kante has had a huge impact
Kante made 175 tackles and 156 interceptions for Leicester last season - more than any other midfielder in the Premier League
Since his move to Chelsea, only Everton's Idrissa Gueye has made more this season
T aking away Kante's ability to break up opposition attacks means teams can get at Leicester's defence more easily now and that balance with Danny Drinkwater has gone
His absence has also seen the work-rate in the team drop
Daniel Amartey is struggling to fill the void and looks like a defender playing out of position in midfield - a passenger at the moment, which Leicester cannot afford
CHAMPIONS LEAGUE DISTRACTION
Leicester's Premier League form is in stark contrast to their results in Europe
The club's maiden European Cup campaign has been a huge success so far with Ranieri's side unbeaten, winning four of their five games, conceding only one goal and qualifying for the knock-out stages as group winners
It is a new and exciting experience for every player and by Ranieri's own admission the focus so far this season has been to qualify for the next stage in Europe
Leicester have found it difficult to maintain the same level of concentration and intensity amid an increased fixture list and their Premier League form has taken the hit
TEAMS HAVE WORKED LEICESTER OUT
Leicester were hugely successful last season by hitting sides on the counter-attack
This term opponents are defending deeper to nullify the threat of Vardy's pace, and it is working
How often this season have we seen that long ball over the top from Drinkwater to put Vardy through on goal? It means Leicester have more possession but Ranieri just does not have enough players to suit playing that way and they are unable to break teams down and unlock their defences
HAS RANIERI RETURNED TO BEING THE TINKERMAN?
In the whole of last season, Ranieri made 33 changes to his starting line-up - the fewest in the Premier League
This season he has already made twice that number
Champions League football has been a major reason for this and so have injuries - the absence of Schmeichel is proving costly
New signings such as Ron-Robert Zieler, Nampalys Mendy, Bartosz Kapustka, Amartey, Ahmed Musa and Islam Slimani were bought to offer something different to the squad and they have yet to be fully integrated
There is no need to panic just yet
Leicester wrap up their Champions League campaign this week until the spring and the focus can return entirely to domestic matters
Ranieri still has the same honest group of players and it is not a lack of effort that is the issue, it is about Leicester rediscovering their intensity and their spark
Until Leicester start to show they are turning a corner, Ranieri will keep being reminded of the statistic about no reigning champion being relegated since Manchester City in 1938
No club is too big to go down - just ask Newcastle and Aston Villa
Source : PA