#1 Luck factor

One of the biggest reasons for the success of Zidane's Real Madrid in the last two seasons was the luck that came their way. Last season alone, the team got 11 points thanks to late winners and equalizers. This season, the team are struggling to score goals, let alone scoring in the dying stages of matches.
Adding to that, Madrid have been robbed off as many as nine points through penalties. As many as 10 penalties, including three in the recent Madrid derby, should have been awarded to Sergio Ramos' team.
Players getting injured at crucial junctures is not helping the team's cause either. Gareth Bale is spending more time in the hospital than on the field, Dani Carvajal's career almost came to a halt when he suffered heart issues but thankfully for Zidane, the right-back has come back with a bang.
Mateo Kovacic is almost match-fit but there is no information regarding the extent of Keylor Navas's injury. Constant injuries to the likes of Sergio Ramos, Raphael Varane, Marcelo, Theo Hernandez etc. have hampered the team's progress this season.