The Portuguese coach lamented his side's lacklustre display as they suffered a surprise defeat at the hands of Getafe to remain without a win in La Liga this season
Los Blancos have now collected just one point from their opening two Liga fixtures of the season and have never previously gone on to win the title after such a poor start, presenting Mourinho with a tough challenge for the remainder of the campaign.
Madrid took a first-half lead through Gonzalo Higuain but some poor defending in the second period offered Luis Garcia Plaza's men a route back into the game, and they duly obliged with strikes from Juan Valera and Abdelaziz Barrada.
"It was an unacceptable game, in this match for me it is not a frustrating defeat. We totally deserved to lose," Mourinho said to reporters after the game.
"There are things that a coach cannot discuss with the press. I haven't talked to the players. They have no feedback on what I think and what I have analysed. I have to talk to them.
"We have worked very hard on defending set pieces, we analyse videos and work on position of each player. But players don't do it.
"The only conclusion that I want them to get is that this was a defeat for Real Madrid and more than a well-deserved win for Getafe."
The Portuguese also queried two key refereeing decisions, claiming that his players said that Adrian Colunga had handled the ball in the build-up to the winner, and also casting doubts over the dismissal of Fabio Coentrao from the bench.
"I have just heard what my players said about the second goal. They said it was handball by Colunga [who assisted the goal]. The referee accused Coentrao of saying a word nobody on the bench heard."
Madrid's shock defeat also saw their run of 24 successive unbeaten Liga matches come to an end, their longest unbeaten stint for 15 years.
Following Barcelona's 2-1 win at Osasuna earlier in the day, Madrid now trail their arch rivals by five points at the top of the standings, and Mourinho revealed his disappointment at such a gap.
"It could be six if we had lost the first game. But we are five [adrift] which is too many points when only six have been contested.
"But today was a different match. Against Valencia we did more to win. Today, we fully deserved to lose."