A club should not underestimate another club, even if the club has a bad performance. Moreover, what we are talking about here is a club like Bayern Munich, which is a club that has above average players who can make everything better. Regardless of their coach being considered to lack experience, I am sure they will always be in tough competition, perhaps what makes the difference is whether they will be able to perform consistently or not.
However, with the squad that Vincent Kompany currently has, there is no reason for Xabi Alonso to underestimate Bayern Munich. Also keep in mind that they will be targeting something big after they failed to defend their title this season. Surely they will have that enthusiasm which will motivate them to be able to play even better than before. Anything can happen next season, so Xabi Alonso must not lose focus which will allow them to decline.
I agree, there is no room for the underestimating other club as things are going any moment can bring changes, and now we are having new generation coaches which are doing good job and having their own way of bringing things under well control and I also sure Xabi Alonso never do any mistake to underestimate them with things could be not easy while we are going to have few changes in all top clubs many new players are joining and giving them strength which will bring good competitiveness and motivation for the success as well.
Even there is too much talk about Vincent Kompany, but we have to watch him before giving any solid comments because he was a good player and also done good job in last job with we can expect Bayern Munich surely could be more aggressive for the future and break their jinx which hurt them badly in last season, and they were ended without any trophy.