Dortmund - Germany midfielder Ilkay Gundogan could be sidelined with a thigh muscle injury when ailing Borussia Dortmund start the second half of the Bundesliga season on Saturday away at Bayer Leverkusen.
Gundogan sustained the injury in a tune-up match in Dusseldorf last week and has not been in team training since.
Also uncertain, although back from Asian Cup and Africa Cup of Nations duty are Shinji Kagawa and Pierre-Emerick Aubameyang. But Japan's Kagawa resumed team training on Wednesday.
The 2011 and 2012 champions Dortmund are second bottom after a terrible first half of the season.
They now hope for improvement starting with Saturday's game at third-placed Leverkusen.