The reason why Arsenal has fallen during Christmas was because they have been maintaining the same pattern of play for a long time which made them very predictable. Now the coach would have a different pattern to execute in the field but there are no subsequent players to use in playing them. Most of their players are on injuries. I could remember Timber, Partey, Tomiyasu, Viera and some other players were on injury quite some period. Although i heard rumours that most of them are back and are ready to play in the competitions.
Arsenal same tactics hurt them badly in last month which bring them down in Premier League but with these injuries are also hurt them now we have few updates with their players are coming back, and they are in market for some changes as well which will bring better results in coming days even now situation is changed but still Arsenal is team to watch in both competitions with if they are able to keep things as needed as surely we will have much better performance in coming matches.
While we have injuries and clubs have no suitable replacements then things can go like this which are surely no ideal but if they are able to have better replacement then we can expect better results but hopefully now Mikel Arteta will learn his lesson and will do things which are needed for staying at the top.