Brendan Rodgers did not hold back about Liverpool's defending following the 3-2 defeat to Udinese on Thursday night.
The Reds looked to be coasting to another three Europa League points after Jonjo Shelvey gave them a deserved half-time lead.
However, the home side found themselves 3-1 down with 18 minutes left on the clock - and a superb free-kick from substitute Luis Suarez was not enough as a late fight-back proved fruitless.
Rodgers gave an honest appraisal afterwards.
"It was very frustrating," he said. "It was a game where we were much the better side but lost our concentration at the beginning of the second half. I thought we'd moved on from that, to be honest.
"We had total control in the first half and were deservedly in the lead, but we were so loose at the beginning of the second half it was frightening.
"Our concentration was very poor and before we knew it we were 3-1 down. The last 20 minutes was very good but it's too late by then.
"I thought we were lazy. Lazy in our play, loose and sloppy.
"We didn't do what I call the dirty bit: we didn't track runners. If you don't do that, if you don't earn the right...
"Whether we thought the game was too comfortable? At this level it never is."
Asked how he could address the defensive problems, Rodgers added: "It's constant reminders and constant work. Some of our play, our movement and passing - you can sense the excitement within the players and the stadium.
"But you can't keep having to score two, three and five goals to win games.
"Defensively, as a group, we need to be better.
"I will be open with my communication with the players, but they are disappointed as well."
The Reds are now third in Group A on three points - with Udinese on four alongside Anzhi, who beat Young Boys 2-0.
Rodgers said: "It is going to be a tight group. There were multiple outcomes in this tournament for us. Obviously we want to qualify but as we've seen in the opening games, some of the younger players who've had the opportunity to play in it are now in the Premier League team.
"Over the course of these next games, obviously we're fighting for the points, but I'm also looking to see if there are one or two other players who can come out of it and help the group in the Premier League campaign."