The loss was Chelsea's third in five games and the Premier League side looked poor in attack and flat-footed in defence when they conceded a counter-attack goal early in the first half.
An angry Tuchel also blamed himself but said it was not the performance he expected after Chelsea narrowly beat West Ham United over the weekend.
"I didn't see it coming, obviously I was in the wrong movie," Tuchel told reporters. "I thought that the last game helped us... I thought the team was prepared, I thought we know what this is all about.
"I don't really know where this performance today comes from. A lack of determination, a lack of hunger and a lack of intensity to actually do the things that we need at the highest level. We are clearly not where we want to be.
"I'm angry about our performance... It's not precise enough, it's not clinical enough, it's not aggressive enough on the ball, it's not determined enough. It's not good enough individually, it's not good enough as a team."
Tuchel said they did not underestimate Zagreb but added that Chelsea losing focus has been the "story of the last few games" where they start well before conceding goals.
"We start okay for 15 to 20 minutes but then lacked determination, precision and maybe even lacked the smell of blood," Tuchel added.
"We conceded a goal with two players in a counter-attack - never happened before. I don't understand why it happened today. It's clearly my job to analyse it.
"We need to be much better... We are not happy with our results, we are not happy with the way we play in general, but I thought we were on a good way. I'm a bit surprised by this performance today."
Catch up with our report from a tough night in Zagreb for Chelsea.
