One way or another, MU could reach the quarter-finals or even the semi-finals because they are unlikely to meet a serious opponent in the earlier stages. This season the Europa League is not as strong as before, there are a lot of average teams that can get in including against MU. Though to be honest, given how MU plays inside the EPL I wouldn't be surprised if they lose to even a weak team
Man United chances are very small compared to other favorite teams, their performance is not yet completely stable, making them not really considered in this competition. Yes, maybe they can make it to the quarter-finals or even the semi-finals, but that would be their best achievement in this competition as they are still behind other teams. In fact, Man United has complete players, but due to the management of the squad not being up to standard, it is difficult for their performance to improve.