Manchester United's performance is difficult to predict and they have played inconsistently this season, but if you look at the match that will take place at Manchester United's home ground, they should play better so as not to be embarrassed by Arsenal at home. Playing at home, there is no guarantee that Manchester United will be able to beat Arsenal, but I believe the match will end in a draw and even if they win, Manchester United will win the match.
Manchester United cannot be considered a weak team. This squad is strong. But the bonding between squad players is weak. Match strategy is not good enough either. This is why United's overall performance has been poor and erratic. So it cannot be said for sure whether United will be able to play well in the home match against Arsenal. Arsenal are in very good form right now. Arsenal have won their last two matches against Tottenham and Chelsea by 3-2 and 5-0 respectively. Arsenal players are expected to continue this trend.
I am not entirely sure if United squad is not weak, feels like they could be a little weak in some positions. Looking at the team, for a whole year and a half, I have been saying that their defense is weak, but seeing this season I could say that their offense wasn't that great neither, I expected a lot more goals from them and they did not, so maybe a wing for this team could be a lot better in the end as well. They are really not seeing the benefits of getting smaller cost players, but more players, instead they go for big budget players and just few players, that doesn't really work that way, it doesn't help them at all.
I personally believe that they shouldn't really spend so much money on few players, but look for young players with higher potential.