The manager now faces the most difficult puzzle of his career so far. With no natural partners for Rudiger, Alonso must improvise radically against elite opposition. The balance of the entire team is now at risk.
The most likely solution involves dropping a midfielder into the heart of the defence. Aurelien Tchouameni has filled the role before, but moving him out of the engine room deprives Madrid of their primary ball-winner. The Frenchman is uncomfortable with the positional nuances of the last line, and exposing him there is a significant risk. Alternatively, Alonso could deploy Federico Valverde in a deeper right-back or centre-back role, but this sacrifices the Uruguayan's relentless energy and goal threat further up the pitch.
Reports suggest the coaching staff may even be forced to field a "Frankenstein" back four, potentially utilising academy product Raul Asencio alongside Rudiger. The lack of cohesion is the primary fear; a defensive line that has never played together relies on communication that simply has not been built yet. In the high-pressure environment of La Liga and Europe, one misstep or miscommunication between strangers at the back usually results in a goal.