The Magpies were outfought and outclassed against the newly promoted side as Teemu Pukki blew the United defence apart with a hat-trick .
Bruce told ChronicleLive: "I would not question the desire.
"I just think we got caught up in their first day (first home game).
"I can't question anybody's desire. I don't think they went out there and done badly.
"But certainly we can do more in a lot of departments. That was the frustrating thing."
Bruce felt that the bouncing atmosphere for Norwich's Premier League return in Norfolk played a part in the defeat.
He added: "We knew all week that Norwich would be playing their first game back in front of a full house.
"We knew how they played last year but didn't do enough to counter that."