LONDON (AFP) - English champions Manchester City slumped to a third shock defeat in four Premier League games at Leicester on Boxing Day to slip to third in the table and seven points adrift of unbeaten leaders Liverpool.
Just a few weeks ago they seemed unstoppable as they started their title defence with a 15-game unbeaten run.
However, a 2-0 reverse at Chelsea has sparked a run of three defeats in 18 days as Crystal Palace and Leicester both came from behind to hand Liverpool a huge advantage in the title race ahead of their trip to face City on Jan 3.
Here, AFP Sports looks at what has caused City's sudden collapse:
1. Fernandinho irreplaceable
City coped admirably in Kevin de Bruyne's absence for most of the campaign through injury thanks to an array of creative midfielders, but have badly missed Fernandinho's ability to play the more destructive role in midfield in the last two games.
The 33-year-old Brazilian had started every league game until Palace's visit on Saturday and is the one player in City's squad without a natural replacement.
Centre-back John Stones deputised at the weekend, while the more attack-minded Ilkay Gundogan was deployed at the base of the midfield in Leicester.
"We have to try and find solutions. Ferna was not able to play because he's injured. We have to overcome this problem," said coach Pep Guardiola, who tried to sign Chelsea midfielder Jorginho from Napoli in the summer as cover for Fernandinho.
"You have to think about how to solve it when you don't have players in a position."
2. Four competitions take their toll
Even for a squad as deep as City's, English football's unique combination of a packed festive period and an extra Cup competition can stretch resources.
Just eight days ago a strong City side beat a much-changed Leicester to reach the League Cup semi-finals and stay alive in four competitions.
Leicester boss Claude Puel claimed victory on Wednesday was vindication for his criticised team selection in the Cup tie with the Foxes fresh to spring surprises over both Chelsea and City in the past five days.
As well as de Bruyne, Sergio Aguero didn't start against Chelsea or Palace due to injury, while David Silva has also been sidelined by injury in recent weeks.
3. Missing Mendy
Left-back has also been a problem position, even as City enjoyed great success last season, due to Benjamin Mendy's knee troubles.
The Frenchman's return to fitness and form in the early weeks of the season promised to give City an extra dimension to their attacking play, but he has been sidelined again since early November.
Fabian Delph, a central midfielder by trade, has filled in at left-back, but is now facing a three-match ban, including the Liverpool game, after being sent off late on at Leicester.
4. Defending the Premier League difficult
Guardiola won three consecutive league titles at both Barcelona and Bayern Munich, but retaining the title in England has proved impossible for any team in the past decade.
A Manchester United side containing Cristiano Ronaldo and Wayne Rooney were the last to do it in 2008-09.
City's record haul of 100 points last season led many to believe they would buck that trend, but it is proving tougher than expected.
"Last season, everyone said it was so easy, but I know how difficult it was," insisted Guardiola.
"Last season we were so consistent and made a lot of points. They (Liverpool and Spurs) are both so consistent."
5. Can City chase?
The question remains whether a Guardiola side is capable of chasing down a title rival to win the league in the manner Alex Ferguson's Manchester United made routine in the 1990s.
In most of Guardiola's seven title triumphs, his Barca, Bayern and City sides have been well in front by this stage of the season.
Now they have to play catch-up and their lack of reaction to going behind to Chelsea, Palace and Leicester leaves City's mentality open to question.
"We have to find an explanation," said Bernardo Silva. "It's mathematically possible, but we have to be almost perfect from now."