Xabi Alonso hasn't proven anything so far so I don't think we can speculate too much, but what is certain is that Alonso is a great coach and he has proven it when he was at Leverkusen and Real Madrid is also a team that has a strong mentality and ethics to play in the Champions League competition, so regardless of the condition of the Real Madrid team, I think they are worth watching out for.
Xabi's Leverkusen antecedent is what most persons will have to bank on at this time, even the Real Madrid management may have used that as a reason to hire him and they sure know he will be needing some time to actually get the team to winning and producing exceptional results. One advantage xabi will be having at Madrid is in the fact that he has ot a team who already has this mentality that is very resilient and can get them to putting up with challenges in anyway it Co.es so he just have to build on that into a squad that will do more than they had in the last season.