The Stamford Bridge boss famously went head-to-head with Madrid legends Sergio Ramos and Iker Casillas while his relationship with Cristiano Ronaldo was also frayed.
In his three-year stint at Los Blancos, Mourinho broke Pep Guardiola and Barcelona's monopoly on the La Liga title but failed to keep a harmonious dressing room at the Bernabeu.
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The current Blues manager dropped Casillas for Diego Lopez, limiting the Spaniard to 19 league appearances. He also publicly criticised Ramos after a defeat to Sevilla.
And in his new book, 'Cristiano Ronaldo', Spanish journalist Guillem Balague explains the moment that changed the Portuguese's relationship with his compatriot forever.
As per the Telegraph, he explained that during the dying minutes of a Copa del Rey quarter-final clash with Valencia - where Madrid were leading 2-0 - Mourinho demanded Ronaldo track back and help his defence.
Back in the dressing room, Mourinho tried to explain his words to the three-time Ballon d'Or winner, but Ronaldo reacted in anger, saying: “After everything I’ve done for you, this is how you treat me! How dare you say that to me?!”
Balague went on to say the manager retreated - seeing Ronaldo was in no mood to back down - before reapproaching the problem some time later.
However, the former Manchester United star, once again, fired back angrily. But this time Mourinho called him out.
Balague wrote: "'Just so you know,' he [Mourinho] shouted for everybody to hear, 'many think like me here, but don’t dare say it, they don’t have the balls to tell you'."
The altercation escalated and Ronaldo had to be held back by a number of his teammates to stop the two 'coming to blows'.
It appeared Mourinho had completely lost the dressing when he left the Spanish capital in 2013; is lightning striking twice for the Portuguese boss at Stamford Bridge?
Will Jose Mourinho still be Chelsea manager by the New Year? Have your say in the comments section below