Well after the jesus injury, I do agree that it would be a lot harder for Arsenal to win the tournament as well. I am not saying that it would be impossible, but it would be a bit harder than usual and it would be a bit more difficult.
I do agree that they do have a big chance, between Juventus, United, Barcelona and Arsenal, these four teams are the big clubs that could have a chance at the title but aside from them I am not sure if there are any teams that could win the title and it could be quite difficult to achieve. Long story short Arsenal is not the biggest candidate to win, whoever wins out of United vs Barcelona will be the biggest chance to win, but Arsenal is not too far from it neither.
First of all I should give an information about Jesus' injury. I have seen on some news sources like Jesus' return will be in early March. If this is true than it is really sad news for Arsenal.
However Arsenal have already proven how strong they can play in Jesus' absence also. Jesus couldn't score any goal after the last match he did on October 1. But Arsenal still didn't get affected by that in a negative way. They still continued to get very positive results by scoring many goals in total. They lost only once which was in a Europa League match. They won nearly all of their Premier League matches in this period of time. This is a proof for how strong they can play as a team even in this kind of situations.
Therefore I'm still seeing Arsenal as the biggest favourite here also.