Following the Reds' 3-2 away loss to Brentford at the weekend, Slot made ten alterations for the fourth-round encounter against Oliver Glasner's outfit. Alongside the wholesale changes to his starting XI, he also packed the bench with youngsters from the academy.
Palace, for the third occasion this campaign, proved too strong for the Reds courtesy of a double from Ismaila Sarr and a subsequent strike from Yeremy Pino. Upon seeing the team sheet, Redknapp confessed his concerns about the youthful nature of the line-up. He also reckons the issues are mounting perilously for Slot.
Following the defeat, which additionally witnessed Amara Nallo receive his marching orders in the closing stages, the pundit declared: "He (Slot) said, 'That was a choice I made, that was the team I picked,' but he picked the wrong team. Make no mistake about it.
"You asked me beforehand and I said, 'He's really made it difficult for himself tonight, picking that team.' He has not helped the young players there, because of the team and the players around them.
"He made ten changes from the weekend against Brentford. You can't tell me he's picked that team today and those subs, thinking, 'That'll get me a result against a really good Crystal Palace side.' You might hope you can, but I did not think for one second they could beat them and he has made a mistake today."
Redknapp also said: "It's not just the defence, it's not just the midfield, it's everything right now. They have got to show some character. They've got some really tough games ahead.
"I haven't said this very often about Arne Slot, because I think he's been sensational, but today was a big mistake. You can't tell me that side was ever going to be capable of beating a really strong Crystal Palace side."
The Reds' youthful team selection could be justified by their upcoming matches against Aston Villa in the Premier League and Real Madrid in the Champions League just days later. In his post-match interview, Slot also confessed there were several injury concerns prior to the match.
With the oldest Liverpool player on the bench being merely 21 years old, Slot said: "I think people who know this club and have followed this club for many years, know that in this competition we use it for younger players. We want to help create a pathway for them to play in front of 60,000 people, in front of our own fans. That is one of the reasons.
"The other reason is because we only have four or five injuries, but if I have to play again the same players. I think there are multiple reasons why we have lost so many games. With all the reasons there are no excuses. But it hasn't been helpful that almost all the time we only had two days in between the games after we had to play away from home."
With a string of six losses in their last seven matches across all competitions, Redknapp conceded the pressure is starting to pile on Slot, his team and his staff. He stated: "He's been unbelievable since he came to the club, but this is real pressure for everybody concerned. This is football and this is the price on the ticket. They climbed a mountain last year, they did something absolutely sensational.
"Now they have to go back to that character they showed last year when they won the title and stick together to get some results. When you ask what's going wrong with Liverpool, there are so many things."