Borussia Dortmund are hoping Mats Hummels will recover from an achilles problem to take on former club Bayern Munich on Tuesday, but Lucien Favre revealed Jadon Sancho is not guaranteed to start.
Hummels had to be withdrawn at half-time in Dortmund's 2-0 win over Wolfsburg on Saturday, as Emre Can made his return from the bench.
BVB sporting director Michael Zorc later revealed the World Cup winner was suffering with a long-standing issue.
Dortmund face defending Bundesliga champions and leaders Bayern at Signal Iduna Park in midweek.
Zorc said of Hummels, who spent three seasons at Bayern before returning to Dortmund: "I spoke briefly to the doctor.