Speaking to Sky Sports, Arne Slot said: "We had to be patient for a goal. It was a very poor performance first half. We were not in the game at all.
"In the end, I had to make some hard decisions at half time to create some anger. The three that came in did really well but I could see from the other eight that they were different.
"I am fully aware you cannot play high intensity for 38 games. Sometimes you have to find another way to win. Hopefully the first half was a warning sign. The good thing is we probably didn't run that much [before facing Paris St-Germain on Tuesday]."