The Germany international aggravated a back problem against Paraguay and is not expected to return for Borussia Dortmund until next month
The Germany international had to be withdrawn during the Euro 2012 semi-finalists' 3-3 draw with Paraguay on Wednesday night due to discomfort in his spinal region.
Further tests upon his return to Dortmund's training ground have clarified the issue and he is expected be sidelined until the end of August, meaning he will miss Bundesliga clashes with Eintracht Braunschweig and Werder Bremen.
A statement on the club's official website read: "Borussia Dortmund midfielder Ilkay Gundogan is expected to be out for two weeks after limping off during Germany's friendly against Paraguay on Wednesday night.
"His back problems, which are a result of a spinal compression, have increased, according to BVB team doctor Markus Braun."
Gundogan will be hoping he can make a full recovery in time for Jurgen Klopp's men's trip to Eintracht Frankfurt on September 1 before another international window opens up.