Dortmund - Bad news for Borussia Dortmund, who will have to do without midfielder for up to a month.

The 22-year-old aggravated a back problem during Germany's friendly with Paraguay on August 14 and was initially ruled out until the end of August, but must now undergo "further rehabilitation" according to club doctor Markus Braun.

Owing to the nature of the injury, the Yellow-Blacks are as of yet unable to set an exact date for the Germany midfielder's comeback.