Erling Haaland faces further tests on muscular problems sustained in Borussia Dortmund's 3-2 win over Hoffenheim on Saturday.
After opening the scoring in the sixth minute at the PreZero Arena, Haaland was forced off in the second half after suffering a knock.
The Norway international will commence treatment for muscular issues this week and now faces a race to be fit for the visit of Bayer Leverkusen on February 6.
A Dortmund statement read: "Haaland was examined in detail on Sunday and Monday. According to the medical report, the Norwegian is suffering from muscular problems, which will require treatment and further examinations in the coming days.
"We hope that Erling will be back to full fitness as soon as possible and can get back to doing what he loves the most – scoring goals for BVB."
Haaland has scored 23 goals for Dortmund in all competitions this season. Only Karim Benzema (24) and Robert Lewandowski (34) have registered more among players from the top five European leagues.
However, among players to have scored more than 10 times, Haaland has the best minutes per goal ratio of 70.4. Lewandowski is a close second with a goal every 71 minutes.