Brendan Rodgers has called Leicester City's defeat to AFC Bournemouth "not acceptable" after the Cherries came from behind to win 4-1 at the Vitality Stadium.
Jamie Vardy netted his 23rd goal of the season in a commanding first-half display for Leicester.
However, after replacing Kelechi Iheanacho with Dennis Praet at half-time Eddie Howe's men managed to turn the game around with a much more spirited second-half performance.
Junior Stanislas tucked away a penalty before Dominic Solanke scored his first two Premier League goals for the club between a Jonny Evans own goal.
With Caglar Soyuncu receiving a red card, the evening on the South Coast will be a night to remember.
"Apologise to supporters"
"Listen, first of all, I apologise to the supporters," Rodgers told LCFC TV. "I don't think I've ever had to do that in my time here.
"We've always been a tough team, mentally and physically, and tried to then play football, but to collapse like we did in the second-half was bitterly disappointing."
Vardy's fourth goal in three games had originally placed the Foxes into a comfortable lead, setting them up for, what looked like, an upcoming victory.
But Rodgers claimed how the momentum shifted to the home side in the second-half.
He said: "[In the] first-half, we had control of the game, scored a goal, looked like we were the threat... and then, [in the] second-half, you expect a challenge from them.
"Especially in the first 10/15 minutes, when you're playing away from home. Sometimes you have to grind that period out and we did that to an extent.
"We didn't show anywhere near the level that you need to, both with the ball defensively. And, like, I said, performance-wise, the attitude was not so good."
"Not a happy changing room"
With Manchester City winning their European ban appeal, City must defeat Sheffield United on Thursday to continue their quest to qualify for the Champions League.
After beating Chelsea 3-0 on Saturday, Chris Wilder's men visit the King Power Stadium in good form and Rodgers believes his side need to "show a greater level of physicality and mentality."
"It's not a happy changing room and it shouldn't be, because that is not acceptable, to deliver that level, especially when you work so well.
"Like I say, it was the attitude. We didn't show the right spirit and that's something that we've showed consistently. But, yes, that was bitterly disappointing.
"[The Sheffield United game] will be a great challenge for us because we need to show a greater level of physicality and mentality. That'll be a really good test."