It seems that everyone already knows which way Sevilla will finish and I think they will be at the bottom. There is no compelling reason other than that at the moment Sevilla is very fragile and will not be able to compete in the group. Most of their opponents are teams that have been very promising since last season and perhaps Sevilla's only advantage is winning the European league. Especially with the absence of goalkeeper Yassine Bounou, it will be easier for Sevilla to break into the goal.
In the group B that Sevilla belongs to, I’m confident they will qualify for the next round of the competition. It may not be as easy as it will be for Arsenal, but I am confident that Sevilla will advance from the group stage ahead of Lens and PSV. These two teams are strong in their respective leagues, but they cannot compete with Sevilla, the defending Europa League champions.
They may have lost several key players in their team, but it will not affect how they perform in the Champions League; after all, they are both European competitions. Not qualifying from the group stage will be bad luck for them because even if they return to the Europa League if they finish third in the UCL group stage, I doubt they can win the title for the second time in a row.