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Hummels had to be withdrawn at half-time in Dortmund's 2-0 win over Wolfsburg on Saturday, as Emre Can made his return from the bench.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. Mats has a complaint with his Achilles tendon.
"He has had this from training for a long time. But we hope that he can play again on Tuesday."
Head coach Favre added: "I can't tell if he will play or not. I hope that he will be back on Tuesday."
Sancho's involvement in the crunch top-of-the-table clash is also in some doubt despite an impressive cameo at Wolfsburg.
The England winger earned his 16th assist of the season as he teed up Achraf Hakimi for the second goal, adding to the in-form Raphael Guerreiro's first-half opener.
But Sancho was again only appearing from the bench, as he had against Schalke, following a calf injury upon his return from the coronavirus-enforced break.
Any assumptions Sancho was simply being rested in order to start against Bayern were seemingly dismissed by Favre.
"He's only been training with the team for 10 days. That is not much," Favre said. "I can't say for sure if he will play on Tuesday."