The Red Devils failed to build on last week’s impressive 5-0 rout of last season’s Champions League semi- finalists as Pierre Emerick Aubameyang’s second half penalty gave Arsenal a first Premier League win at the Theatre of Dreams since 2006.
It was manager Ole Gunnar Solskjaer’s 100th game in charge of the club but defeat means Manchester United have failed to win any of their four Premier League home games this season, leaving them 15th on the table with just seven points.
"It is hard to put a finger on it. We didn't start the game well, gave the ball away far too much in the first half,” skipper Maguire told Sky Sports.
"We can't find excuses so we just have to look within. We were not at it from the start. I don't think the concentration was there in the first half, in terms of the cleanness of the passing. Maybe we were a bit complacent [after the Leipzig win], everybody was patting us on the back.
"But you win and you lose, and you have got to stay level-headed, it is a long old season. I can't put my finger on it. We will analyse it this week. We have another big game on Wednesday [in Istanbul] and we have to move on quickly and we have to improve."
United are back in action against Turkish champions Istanbul Basaksehir in the Champions League on Wednesday.
