I'm wondering what Arsenal will do as of this stage in the Champions League. They had a successful group stage as expected. Now I can say that they have a comfortable matchup to play against Porto as well. Because I don't believe Porto are one of the teams that can eliminate Arsenal in this tournament. Porto couldn't even beat Barcelona in the group stage. I mean that Barcelona aren't weak of course but I don't think they have played better than Arsenal at all. 
Anyway I see Arsenal in the quarter finals already to tell the truth. But they had better improve their performance more as there is some decline recently.
When Arsenal was drawn against FC Porto in the round of 16 of the UEFA Champions League, I expecting Arsenal to win against FC Porto but with the recent performance of Arsenal, I'm not sure if Arsenal could be able to beat FC Porto. If FC Porto can play well in their home, I believe they will beat Arsenal. Anyway I see Arsenal in the quarter finals already to tell the truth. But they had better improve their performance more as there is some decline recently.
Before Arsenal play against Porto in the Champions League, I believe Arteta will correct his mistakes by performing poorly in the league, because it has been a long time since Arsenal qualified for the Champions League, and I believe they will give it their all in the competition, even if they do not win the Champions League, because anything can happen, they can shock people and defeat all the strong clubs and win the trophy, but it will not be an easy task because real madrid, Manchester City and Bayern Munich have a talented players that can compete in any competition.
Arsenal does not have many experienced players who can challenge Real Madrid and Manchester City because, even in the league, Arsenal only has lucky in defeating Manchester City because their key players are injured. Let us see if Arsenal can defeat Manchester City if they meet in the second leg, it will not be easy for them. However, I cannot forecast Arsenal's match against Porto because the game will be extremely difficult, but I feel Arsenal will win if they perform well on the pitch.