You are right that Arteta could easily close the gap if Bukayo Saka is not there but the truth is that Bukayo Saka is one of the best player on the Arsenal team and is very obvious that it will surely affect Arsenal if it happens that he is not there, we all know how important Bukayo Saka has been in every of there matches because he handles his position very well and he knows how to create a scoring opportunity, so actually if there are any Arsenal players that would trouble Manchester City on this match Bukayo Saka is going to be one of them. Although I'm not saying that Bukayo Saka is the only good player in Arsenal but I'm only considering the efforts and assistant he has rendered to Arsenal especially there attacking force. Although all this conversation are just based on assumption because right now Manchester City and Arsenal has ready all there players against there next meeting and they cannot afford to underestimate any player because there both target is to win the match.