The Gunners limited their hosts to just three penalty-area touches in the first half, while just eight per cent of United’s touches in the opening period came in the attacking third.
The midfield-diamond system which dismantled Leipzig was blunt, while Ole Gunnar Solskjaer’s half-time change of shape failed to bring about an improvement.
And among the players who struggled most on Sunday evening was Mason Greenwood.
Without doubt the Red Devils’ most exciting prospect last season, the teenage forward is without a league goal thus far this campaign.
Greenwood burst onto the scene in the Europa League last year and his performances quickly prompted opportunities in the Premier League.
His displays off the bench then led to starts in all competitions and Greenwood’s 17-goal haul saw him supplant Daniel James in the starting XI.
Greenwood had a clear role throughout his breakout season – be it Europa League option, Premier League super-sub or eventually regular starter operating from the right wing, but with the scope to cut inside and use his accurate and fearsome left foot.
He was direct, didn’t overly complicate things and played with confidence; with the ball at his feet, things looked natural and, in stark contrast to James, he always knew in advance what his next move was.
This season, however, Greenwood’s play shows a lack of real identity.
He is yet to play a full match and across his five league appearances is averaging just under 56 minutes per game.
Even after scoring the opener in the emphatic win over Leipzig, Greenwood was taken off just after the hour mark.
The youngster’s lack of minutes means he is struggling to build up a head of steam, while his minutes are split between playing as a centre-forward or having to track up and down the right.
As Solskjaer flickers between formations, it’s difficult for Greenwood to work on his relationships with teammates and develop his game further.
Towards the end of last season, Greenwood dazzled during an extended run in the starting XI, scoring five goals as he lined up in United’s final seven league games.
With a maiden England cap achieved in September and newly-awarded the No. 11 jersey by United, Greenwood was tipped to continue his rapid rise at Old Trafford this campaign.
But his progress has reached a stumbling block. Against Arsenal, he was once again hooked by Solskjaer, this time on 75 minutes after a quiet evening and with a yellow card his biggest impact on the game.
Solskjaer has chopped and changed his personnel up front, with Anthony Martial serving a three-match suspension and Juan Mata enjoying a recent resurgence.
Meanwhile, Edinson Cavani is continuing to build match fitness and is likely in the picture for a league start soon.
That could well spell bad news for Greenwood, who needs the trust of his manager and regular minutes if he is to continue his development.
With difficult trips to Istanbul Basaksehir and Everton up next, Solskjaer’s team selections over the next week may be a telling indication of Greenwood’s status at United.
There is no doubt that the youngster has the talent to star at Old Trafford for the next decade and beyond.
But right now, he needs a little help from his manager.
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