Manager Zinedine Zidane led Real to a record five trophies last year.
But this campaign has not lived up to expectations as Los Blancos sit 19 points behind Barcelona in La Liga.
Modric hinted that the determination and mentality that resulted in so much success in 2017 may have faded.
"The results haven't been what we expected," Modric admitted to FourFourTwo.
"But this is football. Last season things went well, this season we have played quite well but it wan't always enough.
"I have no doubt that it is a temporary crisis and that we will achieve our goals from here to the end of the season.
“The determination inside the changing room to make history was incredible”
Luka Modric
"We are aiming to defend the titles we won last season, and I know it won't be easy, but I will always trust in our quality."
When questioned about the driving force behind last term's glory, Modric gave a behind the scenes insight into the Bernabeu.
"The determination inside the changing room to make history was incredible," he added.
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"We were all motivated to achieve it and were prepared to give our lives for each other.
"Real Madrid has always had a winning mentality, but attitude was key and it helped us in difficult times, for example in extra time against Bayern Munich.
"We always saw ourselves as winners before every match."