"It was very disappointing to lose, especially today and we did not play very well," Queiroz told MUTV.
"We were perhaps too anxious at the start, and that combined with a Manchester City side who showed good movement and were strong on the counter-attack.
"I think the attitude of City and the way we started the game was what influenced the result."
Queiroz also felt the club's below-par performance could be partly attributed to fatigue following a busy programme of international friendlies last week.
"We had seven or eight players who played 90 minutes in a friendly during the week and every time they come back to us they are affected by it in the next game," he said.
"Today I think that was the case and some of our best players who played for their national teams during the week were not as sharp, showed some bad touches, and were not as inspirational as they can be.
"We have a long way to go in the title race and plenty of games in front of us," he added.
"Now we must put this game behind us and start again on Monday. We have not become a bad team after just one game - we are still a good side who can win the championship title.
"It is important we show against Arsenal next weekend this game was an accident and we are still going to challenge for trophies."