Adding to Slot's concern was the lethargic first 45 minutes from his side against rock bottom Southampton in Saturday's 3-1 win that forced the Dutchman into three half-time substitutions.

The Saints, who have won just nine points from 28 games all season, took a shock lead into the break before Darwin Nunez and two Mohamed Salah penalties turned the game around to stretch Liverpool's lead at the top of the Premier League to 15 points.

The League Cup final against Newcastle is also around the corner on Sunday with Slot very much on track for a treble in his first season in charge.

"The first of three finals," he said of the victory over Southampton. "I do hope the next two finals we will play a bit better than the first one.

"The only good thing in the first 45 minutes was that they saved their energy (or PSG) and didn't run at all. It was maybe the first time this season I saw this tempo.

"When I look at the game against PSG, we need to go one step up in terms of intensity. But if I compare it with the game today (Saturday), we need to go three, four, five, six or seven steps up in terms of intensity if we want to have any chance of reaching the next round."

'Going for us'

Salah conceded that he had rarely seeing his manager so furious as he was during a half-time tirade that helped the turn the Southampton game around.

"The manager was like going for us," said the Egyptian. "That's something you need sometimes."

Slot has had little reason to lose his cool in his first nine months as Jurgen Klopp's successor.

But he has shown his ruthless side when needed to keep Liverpool on course for just the fourth treble for an English side that would include the league title and Champions League.

Harvey Elliott scored the smash-and-grab winner in Paris with his first touch after replacing Salah, who had a rare off night.