Real Madrid defence: between Nacho and Varane
The first issue is in defence. There are three cetainties: Carvajal, Ramos and Saturday's goal-hero Marcelo. And then two names: Nacho and Varane. The Academy player has been in the side for six games in a row and his performances in huge games against Bayern Munich and Barcelona show he can rival any of the members of Zidane's squad for a place in the side.
Varane however is in principle the A-Team player for Zidane, but he's coming back from injury just in time for the match. He was rushed back to play at Riazor with Ramos out, and then was left out of the squad for the Valencia match. There were doubts as to whether the French defender was injured, but Zidane said no: "He'll be ready for Tuesday. I gave him a rest so not to push him too hard".
Isco likely to take Bale's place
The second decision Zidane has to take is who to put in for the crocked Bale. Here The Frenchman has a wider range of options: James, Lucas Vázquez, Asensio, Isco... Logic would suggest that the obvious choice is Isco; he didn't play a minute against Valencia after his superb performance at Riazor (2-6 win for Real Madrid) and he's fit as a fiddle.
James, on the other hand, started in the last Liga game, with Asensio coming on in the second half. Despite having barely played in the Champions League then, everything points to Isco starting in Bale's place. Anything else would be a shock that could even indicate his future lies away from the Bernabéu, despite it appearing that he's in line to stay...