5 factors that led to Ole Gunnar Solksjaer's first league defeat as Manchester United boss | Premier League 2018-19

#1 Absence of key players

Mata is one of the many Manchester United players out injured

While Manchester United might have showed great grit to pull off the surprise victory against PSG in the UCL, it must be remembered that the win was achieved without the services of 10 senior first team players, which made it all the more impressive.

Against Arsenal, Solskjaer had to make do without the likes of Alexis Sanchez, Eric Bailly, Jesse Lingard, Andreas Perreira, Juan Mata, Ander Herrera among others, while Anthony Martial was only fit enough to make the bench.

By contrast, Unai Emery had the luxury of being able to choose from majority of his first team squad, as the Gunners have not been hit back with too many injury concerns.

While injuries are very much a part of the game of football, having so many players out at the same time would undoubtedly take a toll on any football club, and this robbed Solskjaer off some useful quality on the bench, which proved detrimental to United's chances of success against Arsenal.