Dani Carvajal started in the first leg but has since suffered a hamstring injury, and with Lucas Vazquez also still sidelined, Alvaro Odriozola is the only recognised right-back that Zidane can call upon.
Nacho Fernandez could play in that role, but the Spaniard may be forced to fill in at centre-back after Raphael Varane was taken off injured against Osasuna, and he has now been ruled out of the game with an abductor issue.
Sergio Ramos could be available for the second leg despite missing out at the weekend, although given his fitness concerns throughout the campaign, Zidane may be reluctant to risk his captain from the first whistle, meaning that Nacho and Eder Militao could pair up in a back four.
Marcelo should be available for the tie despite being called up for polling duty, and there is also optimism over Ferland Mendy's fitness as he aims to shake off a calf issue, with both left-backs included in the squad.
Toni Kroos and Luka Modric are both set for recalls to the middle of the park after being rested against Osasuna, while Federico Valverde has also travelled to London after recovering from coronavirus.
Eden Hazard started on Saturday but may drop out against his former club after an underwhelming showing, while Karim Benzema will hope to overtake Raul as the Champions League's fourth-highest goalscorer of all time following his 71st goal of the tournament in the first leg.
Real Madrid possible starting lineup:
Courtois; Odriozola, Militao, Nacho, Mendy; Casemiro, Kroos, Modric; Asensio, Benzema, Vinicius Jr
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