The visitors won 4-0 with Alexander Isak hitting a hat-trick on the day.
McKenna later said, "Difficult day for us, the opponent was strong and they of course scored the goal in the first seconds which makes it difficult. We had moments during the first half where we had the ball and managed to play through them but overall we weren't able to stop their attacking threats today. They had too much for us.
"I don't think our game management in general was good enough. They are a very good side and we needed to show more resilience and stay in the game until half time and keep the game tight. We didn't recognise the state of the game well enough and we didn't make enough good decisions to stay in the game and attack the second half."
On what he said during half-time, with Newcastle 0-3 ahead, he also stated: "Bits about the first half and how we managed it. There were also opportunities there for us and we were getting into good positions, but it was mostly about needing to show the right characteristics in the second half, show humility, we needed to defend better, we needed to show a better level of organisation and resilience and that we needed to get the next goal. If we had done that then the game could go in one direction. Of course they got the next goal and you are really trying to see out the game in the best way you can.
"We know how well we have been doing to be competitive. It's a huge, huge jump for the group and we don't have to be far off for games to be run away from us. We were off our level. If we do that against a good side like Newcastle then they can open you up. It's a lesson for us. It's probably going to happen a few times in the season."