Christian Eriksen declared Manchester United "lacked courage" after their 6-3 thrashing at Manchester City.
Erling Haaland and Phil Foden both scored hat-tricks for the hosts on the day.
Eriksen said, "It came very heavy. Everyone feels it was a very bad day at the office. We started on the wrong foot. They had chances straight from kick-off. We can only blame ourselves.
"We missed a bit of courage to play out from the back and we let them be at their strength. The main focus from this game will be on ourselves.
"There are a lot of things we need to change and a lot of things we need to do better. Today was far from acceptable from what we should be doing."