Spanish newspaper Marca reported that it was a problem with his hamstring:
Marcelo has broken his left hamstring and will therefore be sidelined for at least two weeks. This means that the player will at the very least miss the Champions League game against Borussia Dortmund and the away game against Real Sociedad at Anoeta.
Carlo Ancelotti confirmed in his pre-game press conference, per @philkitro, that Gareth Bale is not an option at left-back and added that he has more than enough faith in Fabio Coentrao to fill in for the Brazilian.
Ancelotti (on Marcelo's injury): "Coentrao has experience of playing in the Champions League."— Rhiannon Jones (@rhiannoncwjones) April 1, 2014
Sami Khedira, Alvaro Arbeloa and Jese Rodriguez are also missing through injury, although Los Blancos’ injury list is nothing in comparison to their German opponents: Dortmund are without Sven Bender, Marcel Schmelzer, Ilkay Gundogan, Jakub Blaszczykowski and Neven Subotic through injury, while Robert Lewandowski is banned.
Back to Madrid and Iker Casillas will return to take his place as Champions League goalkeeper.
Diego Lopez has come under increased scrutiny on the back of the club dropping from top to third, and another good performance from Iker will increase the calls for the Spanish No. 1 to return between the posts for the remaining La Liga fixtures.
Alongside Coentrao in defence, Ancelotti doesn’t have too many decisions to make.
With Arbeloa out, Dani Carvajal will continue at right-back and the experience of Sergio Ramos and Pepe could mean that Raphael Varane is restricted to a place among the substitutes.
In the middle of the park, with a semifinal spot at stake, the Italian will return to his favoured three-man midfield: Xabi Alonso, Luka Modric and Angel di Maria.
Modric sat out the weekend’s 5-0 win over Rayo Vallecano with flu, but he is expected to make his return to the side, while Di Maria was suspended for the defeat to Sevilla; there have been suggestions Alonso requires a rest, but the Basque midfielder will start.
Up front there is no reason to expect the Italian to coach to orientate away from the BBC.
Ancelotti confirmed, per Marca (in Spanish), that Cristiano Ronaldo’s knee is OK and he has not been affected by the whistling directed at him in the win over Rayo:
[Ronaldo’s] knee is fine. He had a small injury there but it is fine. He has been calm and motivated this week. He has already forgotten the whistles from Saturday.
Bale’s two strikes and his assist at the weekend took him onto 16 goals and 15 assists for the season, per Whoscored, and the Welshman will be looking to have a big effect in a big game at the Bernabeu on Wednesday night.
So far, 14 of his goals have come in Real Madrid wins of two goals or more, while the other two came in 2-2 draws with Juventus and Villarreal.
Between Ronaldo and Bale, as ever, will be Karim Benzema.
Predicted Real Madrid XI: Iker Casillas; Dani Carvajal, Sergio Ramos, Pepe, Fabio Coentrao; Xabi Alonso, Luka Modric, Angel di Maria; Gareth Bale, Karim Benzema, Cristiano Ronaldo