Carlo Ancelotti said criticism of Real Madrid's 1-0 Champions League defeat at Lille was "fair" and that the team "shouldn't look for excuses" after struggling against the Ligue 1 side.
Jonathan David's penalty just before half-time -- after Eduardo Camavinga's handball had been spotted by the VAR -- was the only goal of Wednesday's game.
Endrick and Vinícius Júnior had first-half chances for Madrid, while Jude Bellingham, Antonio Rüdiger and Arda Güler all went close late on.
"The opponent played better, and deserved to win," Ancelotti said in his post-match news conference. "In terms of duels, intensity, consistency. We have to learn what we have to improve, which is quite obvious, it isn't very complicated.
"Today everything was quite bad. We were bad with the ball. It was hard for us to win the ball back. It was hard for us to transition. We needed to be more aggressive.
"The feeling today is that it was hard for us to create. Our possession of the ball was quite slow, with few ideas. We have forwards who need to play more vertically. If it's hard for you to control the ball, and it gets to the forwards slowly, it's a problem."
"I don't know if we lacked aggression, or creativity," goalkeeper Andriy Lunin said. "Maybe we should have fought a bit more. In the second half we were hungrier, we improved."
The result leaves Madrid with three points from two Champions League group phase games so far, and in 17th place in the 36-team table.
"The sadness comes from the feeling of the team, that it wasn't a good game," Ancelotti said. "It wasn't a good night, we shouldn't look for excuses, we have to improve.
"I'm very honest. Criticism for today's game is fair, correct, we have to accept it."
One positive note for Madrid, it was a first Champions League start for Endrick, after the forward scored as a substitute against Stuttgart on his competition debut.
Endrick became the youngest Madrid player to start a Champions League game, breaking Raul Gonzalez's record, aged 18 years and 73 days.
"It's an incredible feeling," Endrick told Movistar. "I'm at the biggest club in the world. It's hard to play from the start. It's very important for me, I'm very happy because of that, but not with the defeat."