Liverpool travel to Paris in a bruised state, having suffered a 4-0 FA Cup quarter-final defeat to City that prompted captain Virgil van Dijk to publicly question his team-mates' commitment.
"You shouldn't give up, and that's maybe, at a certain point, what happened," the Dutch defender said after Liverpool's 15th defeat of a deeply troubled season.
Slot stopped short of agreeing but made the consequences clear. "I didn't see players giving up, but I also think it is good from a captain that he has a strong and firm reaction," he said at a press conference in Paris on Tuesday.
"I can tell you if we have the 20 minutes we had at City tomorrow evening here, we will again concede four goals. So it is a challenge for us to be from the first to the last second at the level we were at in the first 35 minutes."
The stakes are considerable. PSG are European champions, having eliminated Liverpool on penalties in last season's last-16 before lifting the trophy. They arrive in this quarter-final on the back of an 8-2 aggregate demolition of Chelsea and have lost just once in their last four Ligue 1 games. Khvicha Kvaratskhelia leads their European attack with seven Champions League goals this season. Bradley Barcola misses the first leg through injury, but Luis Enrique's side remain heavy favourites.
Liverpool, fifth in the Premier League and already out of the FA Cup, have only Europe left. Goalkeeper Alisson Becker is also absent through injury. The second leg is at Anfield on April 14.
"This year we have been quite experienced in terms of negativity," Slot admitted. "This was a big one because it was a quarter-final. It was a big loss against our rivals."