The likely season-ending injury to Toni Kroos hit Bayern Munich hard. While he's their No. 10, he's not a conventional attacking midfielder. He's a unique player in that, while he is creative and technically proficient, he's not what most people usually picture when they think of a trequarista. His stamina, work rate, defensive skill and his ability to keep the ball allows Bayern to defend from the front better than any team in the world.
His presence was going to be particularly useful against Juventus, who are built around deep-lying playmaker Andrea Pirlo. When teams are able to keep Pirlo's touches down and deny him time on the ball, they're generally successful. When Pirlo gets to run the show, Juventus get the results they want. That's why Bayern Munich blog Bavarian Football Works says that Thomas Müller and Mario Mandžukić will both have to pressure Pirlo in Kroos' absence.
Bayern will be without playmaker Toni Kroos for this match and for the foreseeable future after tearing a thigh muscle in the first half of the last match involving these two teams. Of positive note for Bayern, Javi Martinez will be returning from suspension to reinforce the midfield and defense on Kroos' absence. Expect Thomas Müller to once again be in [Kroos'] usual role of central attacking midfielder, and also expect for him to play much like he did in the first leg. Müller and Mandzukic were essential to the Bayern strategy with their pressing against Juve's Andrea Pirlo.
As BFW notes, the return of Javi Martinez is big as well. He's a much better at ball retention and passing from deep positions than Luiz Gustavo, the man who replaced him in the first leg of this tie. Bayern's attack won't be hurt much by Müller and Mandžukić ending up in less than ideal positions when attacks begin because of his presence.