Liverpool went into their Champions League last-16 tie against PSG last season with a 74.4% win rate under Slot after 43 games.
Since being knocked out on penalties, the Reds have won just 49.2% of their past 59 games, while their loss percentage has more than trebled.
Slot has retained the support of Liverpool’s owners and has credit in the bank after last season’s Premier League triumph – but that is likely to change if they do not qualify for the Champions League.
The Reds either have to win this season’s competition – which seems unlikely after Wednesday’s performance – or qualify through finishing in the top five in the Premier League.
They are currently fifth – one point ahead of sixth-placed Chelsea.
“Slot is not going to get sacked for losing 2-0 at PSG,” said Warnock.
“They are one of the best teams in Europe. But the defeats are stacking up, and there’s the danger there could be more damage next week.
“It is going to suit PSG next week because Liverpool have to go at them.
“They can’t play like this and sit in at Anfield, when they need goals.
“But what does Slot do? Liverpool’s system tonight screams ‘you are better than us’. If he opens up, they leave themselves vulnerable and they could get battered.”
Captain Virgil van Dijk accused the team of “giving up” against City last weekend, when Liverpool conceded four times in the space of 20 minutes either side of half-time.
After losing to PSG, he insisted the team would not give up on their Champions League ambitions.
“We shouldn’t forget we play against the European champions of last season and you see the quality they have in the games that they played already this season,” he said.
“We have to be absolutely spot on with everything we do.
“Hopefully our fans can play a big part in that as well. I’ve been through many special evenings at Anfield, I’m very lucky and privileged, and our fans, that’s the backbone of the club and hopefully they can be there for us again.”