Real Madrid's second Clásico defeat to Barcelona on home turf in the space of four days indicated low morale, according to the former Bernabéu boss.
Ivan Rakitic's 26th-minute goal proved the difference as Barça won on enemy territory for the second time in four days following Wednesday's 3-0 Copa del Rey semi-final triumph.
Madrid are now 12 points shy of the Blaugrana at LaLiga's summit, calling into question whether Santiago Solari will be permitted to continue his tenure as head coach into next season.
Mourinho has been touted for a potential return to the post he left in 2013 and, speaking in his capacity as a pundit for beIN Sports, he identified low morale in the Madrid ranks.
"It was not a happy performance," he said. "It was not the performance of a happy team.
"It was not the performance of a team with great belief and self-esteem.
"Clearly now they are in a zone after a few bad results where they are in a low. They couldn't bring to the game what I used to call the temperature of the big matches. They were passive.
"I cannot speak about a bad performance. I think it's just a soft performance.
"Sometimes you play like this against medium teams and in the end you get a positive result, but against the top teams you have to do much more if you want to win."
Gareth Bale was booed when he made way after an hour, with Madrid's forward line once again demonstrating the considerable shortfall left by Cristiano Ronaldo's departure to Juventus.
"The fact that they lost a player like Cristiano, who scored 40 or 50 goals a season, needs a different approach in the team," said Mourinho, who believes the relative lack of a goal threat across Madrid's front six is a major problem.
"When you don't have a player who scores 30 or 40 or 50, somebody has to score – everybody. A little bit more from everybody.
"[Karim] Benzema was able to give that step. He is scoring more goals, working better than before and looks physically stronger than before.
"But the other players, especially the players from the sides, they are not scoring enough goals.
"At the same time, the midfield triangle is a very positional midfield. Casemiro, [Luka] Modric, Toni Kroos - no one is really a player that does, for example, the run that Rakitic did.
"They are not penetration players, they are players of position. They are passing players, playing with an amazing vision to control the game.
"So they didn't find the right dynamic to compensate for the absence of such an important number of goals."
Mourinho sympathised with Solari's plight of being thrust into the role after Julen Lopetegui's sacking and praised the former Madrid midfielder for harnessing youthful talents such as Vinicius Jr and Sergio Reguilón.
"I think if you can say something in Solari's defence, it is he had the courage to make certain kinds of decisions," he added.
"Because of that courage and that approach you are saying Vinicius is one of the best players of the team.
"I say, from my perspective too, one of the players that could show that Real Madrid traditional desire to compete against Barcelona was another kid like Reguilón, who had a very good approach in both matches."