Real Madrid's defensive crisis has escalated into a full-blown emergency for manager Xabi Alonso after Sunday's chaotic 2-0 loss to Celta Vigo, where star centre-back Eder Militao suffered a serious hamstring injury and defenders Fran García and Alvaro Carreras were both sent off, leaving Los Blancos decimated ahead of their critical Champions League clash against Manchester City.The 2-0 scoreline against Celta Vigo was a difficult result for Madrid, but a major talking point was the injury suffered by star centre-back Militao. The Brazilian pulled up clutching his hamstring midway through the first half, confirming an increasingly alarming situation at the heart of Madrid's defence. He could be out for around four months, according to AS, and the blow comes as a significant setback, coming just as Alonso needed his most dependable defenders available for a demanding run of fixtures.Militao’s importance to the side cannot be overstated. His pace, aerial dominance, and recovery skills are central to how Madrid defend, allowing the full-backs and midfield to operate higher up the pitch. His early departure immediately unsettled the side, a fragility only compounded later in the game by the rash decisions that led to red cards for both Garcia and Carreras. This trio of incidents has exposed a severe lack of cover and discipline, turning a potential speed bump into a major crisis of availability. As the team look ahead to crucial La Liga and Champions League clashes, the loss of Militao changes the entire complexion of their defensive strategy.Militao’s hamstring issue adds him to a treatment room already overflowing with world-class talent. Trent Alexander-Arnold, the high-profile summer arrival who was meant to revolutionise the right flank, remains sidelined with a persistent thigh injury that has severely disrupted his debut season. Veteran leader Dani Carvajal is out for the long term following knee surgery, removing a vital voice from the dressing room. Meanwhile, David Alaba remains a major doubt as he battles recurring muscle problems that have kept him out for weeks.The depth options are equally ravaged. Ferland Mendy is unavailable with his own fitness concerns, and young centre-back Dean Huijsen is struggling with a muscle strain picked up in training. When you factor in the suspensions of García and Carreras, the manager is left with Antonio Rudiger as his sole fit, senior centre-back. It is a defensive crisis that leaves the squad bare bones exposed, forcing the club to look at emergency measures just to field a starting XI.Looking for smarter football bets? Get expert previews, data-driven predictions & winning insights with GOAL Tips on Telegram. Join our growing community now!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.The timing of this crisis is merciless. Real Madrid are staring down the barrel of a pivotal Champions League clash against Manchester City. The prospect of Erling Haaland and Phil Foden running at a patched-up Madrid defence is enough to keep any supporter awake at night. Guardiola will undoubtedly instruct his team to press the inexperienced or out-of-position defenders, looking to force errors in the build-up. Without Militao’s recovery speed or Carvajal’s experience, the Blancos backline will be vulnerable to City's rapid transitions.Alonso will at least have Carreras and Garcia available for selection against the English club, but his options remain depleted and both players will be out for their next La Liga match, causing further concern for a side sitting four points behind Barcelona in the Spanish top-flight.