If Atalanta is able to beat Bayer Leverkusen, then playing in the Champion League which basically Bayer Leverkusen will playing against teams with better quality, then of course Bayer Leverkusen still has to bring in new players. At least, to prepare the team to be even better next season with the best possible rotation that can be done if Bayer Leverkusen brings in some new players. Although indeed, I also still recognize that Xabi Alonso will still be able to provide good results for Bayer Leverkusen next season but it seems, only limited to the domestic league. Because anyway, if they want to get good results also in the Champion League, then total rotation will be something that must be done, so they need second-tier players who also have good quality.
Leverkusen is showing a pretty good performance at the moment in the Bundesliga, but on the contrary the first defeat of the season they got in the Europa League against a team that has never been the favorite to win the Europa League, the defeat to Atlanta of course indicates that the mentality possessed by Leverkusen is not enough to compete in the current European competition, this season Leverkusen failed in Europe after the lack of mentality they have so that our doubts arise To be able to see them go far in the Champions League next season, as you said, of course at the moment Leverkusen still needs to improve the quality of the squad they have to maintain their Bundesliga champion status and also compete in the Champions League next season.
Currently it is reported that some Leverkusen players are starting to be approached by big European teams, so if Leverkusen loses some of their main players this season, of course it will be very risky for Leverkusen, in addition to having to maintain the current squad, of course Leverkusen must bring in several other players who are able to improve their mentality and performance next season, I personally see if maybe Leverkusen is still able to compete in the top 4 of the Bundesliga next season, but competing for the title again certainly seems impossible because currently Bayern Munich is starting to improve their squad.