Dortmund - Liverpool manager Jurgen Klopp is waiting on the fitness of Reds' captain Jordan Henderson after the midfielder was forced off in their Europa League quarter-final draw at Borussia Dortmund.
The full extent of Henderson's injury will only be known after a scan on Friday.
"He's injured his knee. It's not a small matter and it doesn't look good," said Klopp.
"We'll have to wait on the results of a scan."
The 25-year-old Henderson failed to come out for the second half at Dortmund's Signal Iduna Park stadium and was replaced by Joe Allen in the 1-1 draw.
Liverpool claimed a precious away goal when Belgian striker Divock Origi slotted home in the first-half before Dortmund equalised after the break with a header from captain Mats Hummels.
Henderson is likely to miss Liverpool's next home game against Stoke City on Sunday and the second leg of the quarter-final at Anfield next Thursday.