Santa Cruz was injured on international duty for Paraguay in early September but, following a cartilage operation, had made better than expected progress. However, after returning to training on Sunday, he found his knee could not cope and began swelling up.
The 23-year-old travelled to see a specialist in Augsburg, where doctors opened up his knee again to examine the problem. With more surgery needed, the striker will be out for some time and no date has been set for his likely return.
There was more disappointment for 20-year-old midfielder Trochowski. The German Under-21 international has been struggling with a knee complaint which Bayern's medical staff initially tried to treat conservatively. However, the persistent nature of the injury means that he too requires an operation and faces a lengthy lay-off.
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