Claudio Ranieri says Leicester "must do something" defensively after they conceded "two strange goals" in the first half against Chelsea.
Diego Costa was given the freedom of half of Leicester's penalty area to score after seven minutes on Saturday before Eden Hazard and Victor Moses completed a 3-0 victory for the hosts, extending Leicester's miserable start to the defence of their unexpected title.
The Foxes were robust last season, but have now conceded a league-high five goals from corners this term.
Leicester boss Claudio Ranieri said: "We have to do something. It's not a name, it's not who's playing or not, it's the concentration. Now too many times we concede a goal from set-plays.
"The first half the performance wasn't good. We conceded two strange goals. The first corner, [he] was alone. It's not me alone [it was] Costa. It's not easy to leave him.
"The second was a ricochet. It was unbelievable what happened this season."
Leicester have eight points from eight games in a similar post-title malaise to Chelsea's of last term, but Ranieri is focused on working to respond.
"I'm not worried. I know my job," he said. It's difficult to say what happened this season. You see it's a different Leicester.
"Also me and my players - we see it's a different Leicester. Now it's important to understand why."
Ranieri acknowledged Leicester's first foray into the Champions League has had an impact, but still demands the same level of concentration domestically.
The Foxes play Copenhagen on Tuesday night and Ranieri rotated his options with that game in mind.
Riyad Mahrez did not start a Premier League game for the first time in a year, while Islam Slimani and Danny Simpson were also dropped to the bench.
But the Foxes boss insisted he would make the same decision again.
He added: "The Premier League is one year long. Champions League is two months, in or out.
"We want to go in the knockout in Champions League or Europa League. To achieve this you have to have all your players fit and I prefer to preserve some players for Tuesday night."
Ranieri denied suggestions resting players sends out the wrong message.
"If Chelsea is not an important match, you have to close the bar or the pub," Ranieri added.
N'Golo Kante turned down Champions League football with Leicester to move to Chelsea and showed his former employers what they were missing with a fine performance.
But Ranieri downplayed the loss of the France midfielder.
"Kante wasn't in our box last season when we have the corner [to defend]," he said. "Of course N'Golo Kante was important for us, as were all the other players.
"[But] it's not only one man that changes the team. It's the brain [mentality] that change the team."