Bayern did not specify the duration of his unavailability but according to Sky it could be "between six and eight weeks" which would rule the 27-year-old German international out of contention for the season-opener at Frankfurt on August 5.

"The FC Bayern medical unit diagnosed an abnormality in the Germany international's left knee, which was removed arthroscopically today (Monday). The operation went according to plan and was completed successfully," the club said in a statement.

After making himself a mainstay of the Bayern midfield, Goretzka missed several months last season due to knee problems.

Bayern have already signed Ryan Gravenberch from Ajax as a ready replacement. And according to German media, the club could also strengthen the midfield by bringing in Konrad Laimer from RB Leipzig.

Bayern are currently in the United States where they will face DC United on Wednesday and Manchester City on Saturday.

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