Paco Alcacer scored on his competitive debut for Borussia Dortmund, but coach Lucien Favre revealed the forward suffered an ankle injury against Eintracht Frankfurt.
Alcacer joined Dortmund on loan from Barcelona late last month and his debut on Friday was a successful one.
The Spain international was involved in Marius Wolf's goal and later struck from 20 yards to seal Dortmund's 3-1 win, after Abdou Diallo's opener was cancelled out by Sebastien Haller.
Favre said the 25-year-old still needed time, before revealing Alcacer hurt his ankle late at Signal Iduna Park.
"He hasn't played all that much recently.