For a team with an aging corps of rightbacks there isn't a ton of room for error. And when your rightback, and Hinrunde leftback, Rafinha goes down injured in a meaningless friendly it removes all the room for error.
Rafinha was substituted in the 66th minute of Bayern Muncih's match against Karlsruhe after going down with a non-contact injury. The injury came following a Karlsruhe attack and Rafinha was immediately substituted for by Niklas Dorsch. Rafinha was immediately evaluated on the sidelines by trainers who paid specific attention to his knee. Rafinha left the field and returned to the locker room under his own power.
Hopefully this is just a precautionary move from Bayern Munich, but the non-contact nature of the injury is an extremely worrying signal. Life without Rafinha will be extremely difficult for a team who came into this season searching for an extra rightback and didn't get one. An injury to Rafinha would leave Bayern Munich with just Philipp Lahm capable of manning the right side and no depth behind him.
UPDATE: Bayern Munich have confirmed that Rafinha sustained a knee injury. They have yet to release a full diagnosis or timeline for his return.