Georginio Wijnaldum admitted Liverpool were caught cold by Leicester City's spirited display in their 3-1 defeat at the King Power Stadium on Monday.
Two goals from Jamie Vardy and a brilliant strike from Danny Drinkwater put the Premier League champions 3-0 up after an hour, with Philippe Coutinho's effort coming as scant consolation for the visitors.
Manager Jurgen Klopp was left angry with his side's display, the defeat meaning Liverpool remain a point outside the Champions League places, having played a game more than Arsenal in fourth.
And Wijnaldum confessed the players did not heed Klopp's warning prior to the match, as they allowed themselves to be overrun by a Leicester side determined to impress in the wake of Claudio Ranieri's departure.
"It was really difficult," Wijnaldum said, as quoted by Liverpool's official website. "We knew beforehand that it was going to be tough, especially in the first couple of minutes, but we didn't adapt well in the game.
"They were playing really hard in the beginning; you could see it in the first couple of minutes when they made the tackle on Sadio [Mane] - that was a sign that it was going to be a really difficult game.
"We didn't adapt well in the situation, and then we went behind 1-0 with a mistake from me. Then we were not in the game. We scored a goal, but at the end it wasn't good enough from our side.
"It's really sad. The manager told us already at the beginning of the week, and again when Ranieri [left], that it was going to be a really difficult game.
"They wanted to show that they are a good team and they wanted to fight to beat us. We were not ready at the beginning of the game."
Liverpool face Arsenal in what could prove to be a pivotal match in the race for the top four on Saturday, and Wijnaldum is aware of the need to respond following their latest setback.
"After every defeat it's important to bounce back," he added. "That's what we have to do on Saturday."