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 expected 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.
I don’t think Arsenal recent decline in performance will be replicated in the champions league. The champions league is a different game to the premier league that they’re underperforming now. With the team they’ve been matched up with, their confidence level will improve and they will try everything possible to win in this match. FC Porto are not a very tough term but they are not also a weak team that can easily be beaten in the champions league. For Arsenal to win this match, I expect them to put more efforts into the match and not play the way they’re playing currently in the premier league. I also see Arsenal in the quarter finals already, because despite their decline in performance, they should be able to pass through FC Porto either the easy or hard way.
But Arsenal have fallen heavily over Christmas so far, taking just 1 point in the last 3 Premier League rounds and having just been eliminated from the FA Cup by Liverpool. Arsenal is still a strong opponent, but Mikel Arteta's decisions often cause the team to fall into a "self-destructive" position. With the current situation. Mikel Arteta must increase staff after the record summer transfer spending in the club's history. I think Arsenal is lacking a class striker in the squad. I really want them to sign Brentford's Ivan Toney or Napoli's Victor Osimhen. And they need quality players on the bench who can make a difference.