#3 Bernd Leno's mistakes
Bernd Leno has been in good from this season. Since Petr Cech's injury, he has been pretty solid between the sticks for Arsenal.
However, in recent times he seems to be making mistakes leading to goals. In the game against Tottenham a couple of weeks back, he was largely at fault for the first goal scored by Eric Dier, due to his failure to deal with a close range header by the Spurs midfielder.
In the game against Liverpool at the Emirates some weeks ago, his failure to deal with a harmless cross gave James Milner room to shoot at goal, putting The Reds ahead.
In the game against United, he was partly at fault when he parried a free kick unconvincingly, which fell to a United player who squared the ball for Martial to draw United level.
He looks a bit complacent at times, which is something he has to watch because Petr Cech will be ever ready to reclaim his place as Arsenal's #1.