European champions Real Madrid have been usurped by Barcelona at the top of La Liga for the first time in five months.

Los Blancos slumped to their fourth defeat in 14 games in 2015 as Aritz Aduriz's thunderous header handed Athletic Bilbao a 1-0 win over Los Blancos on Saturday, whilst Barca were rampant in destroying Rayo Vallecano 6-1 on Sunday thanks to a hat-trick from Lionel Messi.

After ending 2014 with four trophies on the back of a 22-game winning run, AFP sports looks at what has gone for Carlo Ancelotti's men since the turn of the year.

1. Injuries

Even for the most expensive squad ever assembled in the history of football, a spate of injuries to key players, particularly Luka Modric and James Rodriguez, has left devoid of options in midfield.

Meanwhile, Sergio Ramos's leadership in defence has been badly missed during his month-long lay-off due to a hamstring problem.

2. Lack of squad depth and rotation

The impact of those injuries have been exaggerated by Ancelotti's refusal to rotate when things were going well at the start of the campaign and the sale of Xabi Alonso and Angel di Maria just before the season got under way.

Fatigue of playing every game, particularly after a World Cup summer, is beginning to take its toll on the likes of Toni Kroos and Karim Benzema.

3. Ronaldo's Ballon d'Or dip

Even by his own stunning standards, Cristiano Ronaldo's goalscoring rate in the first half of the season was barely believable. The Portuguese scored 32 times in 25 games between August and December to propel him towards a third Ballon d'Or in early January.

In 2015 that ratio has fallen to seven goals in 12 games, two of which have come from the penalty spot, whilst Messi's hat-trick means the two are now level on 30 league goals apiece when the Argentine trailed the Portuguese by 12 three months ago.

Ronaldo also saw his ninth career red card in that run for kicking out at Cordoba defender Edimar and suffered a high-profile split with long-term supermodel girlfriend Irina Shayk off the field.

4. Bale's longest Madrid goal drought

Just when Madrid have most needed Bale to step up as Ronaldo's form has dipped, the Welshman is in the midst of his longest goal drought since swapping Spurs for the Spanish capital 18 months ago.

Bale hasn't found the net in over 720 minutes of football and at times seems hesitant about going for goal after criticism in the Spanish press for being too greedy at the start of the year.

5. Ancelotti not the man for the long haul

Just three months ago Real president Florentino Perez was making suggestions that he wanted the Italian to be Madrid's Alex Ferguson, the legendary Scottish manager who led Manchester United for 26 years.

Now there are doubts whether Ancelotti will be in the job 26 weeks from now if he fails to deliver a major trophy at the end of the season.

Ancelotti responded to criticism of his easy going management style on Friday by saying it had helped him to win three Champions Leagues - including ending Madrid's 12-year wait for their 10th European Cup last May.

However, Ancelotti is far from as specialised when it comes to the long-term league format where he has won just three league titles in his previous 15 seasons at top clubs like Juventus, AC Milan, Chelsea, Paris Saint-Germain and now Madrid.