Craig Shakespeare had to watch his side blow two leads in the Premier League opener against Arsenal on Friday.
Twice Leicester City went ahead, but a late collapse saw Arsenal score twice in the final 10 minutes to take a 4-3 win.
After the match, the Foxes' boss faced questions about his use of substitutions, with Kelechi Iheanacho coming into the match just before Arsene Wenger's side leveled through Aaron Ramsey from a corner, but pointed to the defending of set-pieces as the real issue.
"I think when teams make substitutions from the corners, it can cause a bit of confusion. That's not making any excuses because when subs go on, they are given jobs and I expect them to pass on information," he told Sky Sports.
"If you look at the third goal, I'm a bit disappointed with the handball leading up to it but that aside, once you get the corner, you have to defend it better.
"I don't know whether it was a lack of concentration or just a lack of game management in the last ten minutes, but you then concede again from a set play in terms of being overpowered. We need to show a bit more resilience there.
"I went to a three-man midfield to get us a screen because Mesut Ozil was playing in the pockets and I wanted Wilfred Ndidi to get in and around him. I then wanted Wilfred and Daniel Amartey to get up close to their midfield players and for Iheanacho to have the space in the last ten minutes to get on the back of Granit Xhaka.
"Of course, I have to look at my own decisions but you make those decisions for the right reasons. Ultimately, it wasn't that which cost us, it was the set plays."
Arsenal's winner also came from a set-piece, with Olivier Giroud heading home.
Leicester return to Premier League action with a home match against Brighton on August 19, while the Gunners travel to Stoke on the same day.