Pep Guardiola admitted he made "too many changes" as he took the blame for Manchester City's 2-0 Champions League defeat at home to Bayer Leverkusen.
Guardiola sprung a surprise by swapping out 10 players from the weekend's 2-1 defeat at Newcastle, leaving Erling Haaland, Phil Foden and Gianluigi Donnarumma among others on a star-studded bench.
But those that did come in to the side failed to take their chance as Alejandro Grimaldo finished a quick Leverkusen counter-attack in the 23rd minute and, even after Guardiola introduced Foden, Rayan Cherki and Nico O'Reilly at the break, Patrik Schick added a second eight minutes after the restart.
"Too many changes," Guardiola said. "I always believed in long seasons every two days, everyone has to be involved, but maybe it was too much. Seeing the result, they played not to make mistakes instead of playing to do what we had to do.
"When you are thinking to avoid not punishing the team you are not free to be relaxed - with or without the ball. We were close but not aggressive enough and they are a really good team...
"I take absolutely the responsibility but I saw them and I like everyone to be involved. When you are a football player and don't play for five, six, seven games it's tough but maybe it was too much."
Guardiola admitted his regular starters would most likely have played with more confidence but when asked if this performance raises questions over his squad depth, he demurred.
"It was the first time in my life I've done it and it was too much I realise."
"It's impossible to think that they are not good," he said. "I need everybody as part of the group.
"I felt from my instinct, from my gut, that the team is training good, they have incredible vibes so let's go - Champions League at home, we are in a good position.
"For the next games we have Fulham, Sunderland, (Real) Madrid, a lot of games together. We cannot play all the time, Erling, for 95 minutes. It was too much. It was the first time in my life I've done it and it was too much I realise."
Asked if Guardiola's team selection suggested he had underestimated his side, Leverkusen coach Kasper Hjulmand said: "I don't think so. It's a very tight programme for all the teams. I think in the Champions League the normal rotation is 5.5 players.
"This time it was a bit more but no matter who they put on the pitch it's a quality team."
City loanee Claudio Echeverri was an unused substitute for Leverkusen amid suggestions the 19-year-old could be recalled in January due to a lack of playing time, having made only three starts in eight appearances all season.
"We like Claudio, we are happy to have Claudio," Hjulmand added. "I think when he arrived to us he had only played 110 minutes the whole year...We are trying to build a young player with great potential.
"We like Claudio, we like him in the dressing room, we like him on the pitch. We can see the potential so let's see."
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