Claudio Ranieri gambled on a second-string team for this dead rubber and was given a lifeless display that cranks up the pressure for Leicester’s Premier League return.

The Foxes were humiliated by the Dragons of Porto, a result that does not affect the club’s progression as Champions League group winners but inflicts a deep wound on a near-perfect campaign in this competition.

After five unbeaten games with one goal conceded, here was a demoralising defeat where five goals went in at one sitting.

Ranieri made 10 changes to his starting XI, with an eye on Saturday’s visit by Manchester City, and had wished to see those who were given a chance present him with a selection dilemma.

Nothing of the sort transpired. This was the worst defeat by an English side in the European Cup’s 61-year history and afterwards Ranieri accepted responsibility, but delivered a razor sharp warning to those he trusted here in Oporto.

They had ‘missed a great chance’ to impress, he said, and cannot now knock on his door to argue for a place in the battle against relegation.

‘I have no regrets because I wanted to give an opportunity to all my players,’ he added. ‘But it was too easy for Porto. I am very, very sad. OK we can lose, but not in this way.’

Given Real Madrid, Bayern Munich and Paris Saint-Germain are among the sides Leicester could pull out of the hat in Monday’s last-16 draw, a dramatic improvement is required.

And while the big names will return for that tie in February, Ranieri’s immediate concern is triggering an upturn in domestic form.

With Jamie Vardy, Riyad Mahrez and Robert Huth among those left at home, only Wes Morgan survived from the defeat at Sunderland four days before as some rarely seen faces populated the team.

Ben Hamer’s inclusion in goal was perhaps the most surprising, the 29-year-old’s last senior game coming in August 2015 for Bristol City in a Championship defeat by Burnley.

There were Champions League debuts, too, for Ben Chilwell, the highly rated 19-year-old left-back, and Nampalys Mendy, who was playing for the first time since August after an ankle injury.

Wearing an unfamiliar red strip, Leicester looked impostors, went behind within six minutes and produced a passive performance that should trouble Ranieri, even though this match didn’t matter in any material sense.

Another set piece undid them in the simplest of ways. Jesus Corona delivered an outswinging corner and Andre Silva powered a header down and in. Not including penalties, the goal was the seventh Leicester have conceded from a dead ball delivery this season.

In the 26th minute the lead was doubled in outstanding style. Alex Telles produced a deep cross that went beyond Chilwell and found Corona, who struck the ball on the volley with such timing it flew into the roof of Hamer’s net.

Leicester’s misery was compounded a minute before the break when Corona slipped Maxi Pereira in on the overlap and his cut-back was met with a delightful flick by the unmarked Yacine Brahimi.

The defensive door Leicester had kept tightly shut for the first four games in this competition, pushed ajar against Club Bruges, was barged down here. Porto are a technically gifted side but goals have not been their forte recently — just three in eight games prior to Wednesday night.

Leicester finished the first period with only 32 per cent possession and for the start of the second, Ranieri sent on Leonardo Ulloa and Marc Albrighton. But Leicester remained limp, Porto scoring a fourth after the hour.

Referee Felix Zwayer judged Danny Drinkwater had pulled down Silva in the box and the striker sent Hamer the wrong way from the spot.

Harvey Barnes, an 18-year-old midfielder, gained his first taste of senior Leicester action as a late substitute but 13 minutes from the end a dispiriting experience for Leicester was underlined when Diogo Jota ran through and finished through Hamer’s legs.