Borussia Dortmund centre-back Neven Subotic faces a potential injury lay-off after suffering a suspected torn cruciate knee ligament in Saturday's 2-1 Bundesliga defeat at Wolfsburg.
The Serbia international came off after 45 minutes at Wolves and coach Jurgen Klopp said the 24-year-old had "probably" torn his cruciate ligament.
"It's terrible news," Klopp told German Sky Sports. "Our doctor still has to organise a scan and we'll find everything out then."
Second-placed Dortmund host European champions Bayern Munich in the Bundesliga in a fortnight in a repeat of last season's Champions League final with the Bavarians four points clear at the top.
Four days later, Dortmund host Napoli in a crucial match in the Champions League where they are third in Group F having lost 1-0 at home to Arsenal last Wednesday.
Dortmund have only just welcomed Subotic's centre-back partner, Germany's Mats Hummels, from a back injury, but Borussia can rely on Greece defender Sokratis Papastathopoulos as cover for Subotic.