Gareth Bale sat out at the weekend with flu, having only been fit enough to come off the bench in the first leg last week.
He may well return here but if he isn't fit, Angel Di Maria will play on the right wing with Isco in central midfield.
Marcelo will play at left-back despite Fabio Coentrao's man of the match performance at the Bernabeu last week.
Bayern are in the unfamiliar position of having to win and avoid conceding an away goal, after having lost the first leg of this tie. They dominated possession but lacked incision, struggling to break Real Madrid down or defend against their counter-attacks.
Carlo Ancelotti won't be able to set his team up to merely soak up pressure for 90 minutes, and will have to go looking for that vital away goal. They are lethal in attack and Bayern would do very well to stop them from scoring at all.
Bayern will start at tempo and it will probably be a question of how long Madrid can hold out. Nonetheless, with Bayern pushing for goals, they could leave themselves open at the back and Ronaldo and co will punish them.
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