Jamie Carragher said Arne Slot got his tactics "massively wrong" and that Virgil van Dijk will be pleading with him not to use a back five again after Liverpool were outclassed by Paris Saint-Germain.
Liverpool were left with a huge task to reach the Champions League last four after a 2-0 quarter-final first leg loss to the holders which, according to Carragher, could easily have been "five or six".
Desire Doue and Khvicha Kvaratskhelia were on target as Luis Enrique's side condemned Liverpool to a 16th defeat of the season but they missed a succession of chances to further extend their lead and also had two penalty appeals turned down by VAR.
Liverpool took Paris Saint-Germain to penalties at the last-16 stage last season but Carragher was alarmed by the extent of PSG's superiority a year later as the Reds' poor season continued.
"That was like watching a team from a lower division," he said on CBS Sports Golazo. "The gulf in class was very worrying from a Liverpool point of view.
"In some ways, it's a great result as it should have been five or six. But the gulf between the two teams was absolutely startling when you consider last season.
"Yes, Liverpool got battered at PSG and they won 1-0, we know that. But the second leg at Anfield was a really close game, two top teams.
"Liverpool then go and spend £450m, probably a lot more than PSG spent in the summer. To see the gulf there is worrying. You think, 'how's it got to that? How's it got that bad?'"
Slot switched to a back five in an attempt to contain the threat of the French giants but Carragher felt the decision backfired due to an insistence on using man-to-man marking which left Virgil van Dijk exposed alongside the struggling Ibrahima Konate.
"The manager has tried something but he's got it massively wrong tactically, how he went about it," Carragher continued.
"It's easy for me to say that, after the event, but that's what we do, we're pundits, we speak after the events in the game.
"They were actually more open with the back five than they would be with the back four because they went man-to-man all over the pitch and the three centre-backs had to cover the width of the pitch.
"Watching Virgil van Dijk tonight in the middle of the back three… Normally, when you get to a certain age, you think, middle of a back three, that's perfect for me, everyone's in position, you get a bit of protection in your back five.
"This was different. Defenders were jumping into midfield. There was no one to mark. And Van Dijk, at 34 years of age, was having to run in there and run across. He couldn't do it.
"People have criticised Van Dijk this season for his performances and I think it's been harsh. He plays every game. The fella next to him has been awful all season and was poor again tonight, Konate. He makes a mistake every game.
"That's not easy to play alongside. I actually think Van Dijk has been one of Liverpool's better players but tonight in that back three, I have never seen him so uncomfortable in a Liverpool shirt in my life.
"I think he will be pleading with Arne Slot to never play that system ever again because he found it so tough.
"But, what I must also say is that it's not just the system of Liverpool and getting it wrong tactically, PSG were absolutely out of this world. It was like watching Pep Guardiola's Barcelona."
Slot was relieved to at least keep the tie alive but agreed with Carragher's assertion that Liverpool were fortunate not to be beaten by a bigger margin.
He told TNT Sports: "We're lucky to only lose 2-0 as they had more chances than they scored, although the first goal felt harsh as we didn't give anything away.
"It's very good we're still in the tie. We can bring them to Anfield with how much a difference Anfield can make for us.
"We wanted to create much more but there wasn't a lot to create for us. They were having the ball with incredible tempo all over the place.
"We tried to press them high. Sometimes it was working but lots of times they were able to play through us.
"When we went man-for-man they played the ball in behind us. When we were in a low block we hardly conceded although the goal was when we were in a low block.
"I stood here similar last season and although we won 1-0, the game was exactly the same. But the game at Anfield was completely different, so we're happy we're in the tie."
Slot also explained his decision to leave Mohamed Salah as an unused substitute having omitted him from his starting line-up.
He said: "I think the last part of the game was more about surviving for us than there was ever a chance we could score.
"I think this was a 20 to 25 minutes where we were only defending.
"Mo has so many qualities but him defending for 20 to 25 minutes in his own box, it's better to save his energy for the upcoming games."
