Xabi Alonso is prominent enough to handle the hurdles which will be coming his way next season. Remember he's the main reason behind the sudden peak form of Bayer Leverkusen, they're able to comprehend the situations at hand and hitting top target in each season. Bayer Leverkusen have relaxed their players and they're warming up for the big season ahead. This is not an easy one because the entailed actions involves other oppositions.
I also have no doubts about the ability of Xabi Alonso especially for this season again because from what he has shown last season at Bayer Leverkusen to be able to win the Bundesliga is something extraordinary so that it has been a good achievement for him and hopefully can be achieved again this season. However, I do not think that Bayer Leverkusen can easily face the obstacles in the UCL, because it is a competition with quite high tension and very different from any competition including the Bundesliga.
Honestly, although I believe Alonso is able to maintain the quality of the Leverkusen squad, I am a little doubtful considering that every season there must be changes. These changes are either for the better or even for the worse and it happens not only to Leverkusen but to all teams in the bundesliga at the moment. Maybe Leverkusen can maintain the stability of the team's performance, but if there is another team that is more experienced in making bigger changes, it will certainly be more difficult than last season. And now Bayern Munich looks more ready to restore the title dominance that was once broken by Leverkusen. So the competition this season will not be as easy as last season and of course Alonso needs a more appropriate strategy.