Liverpool manager Jurgen Klopp is waiting on the fitness of captain Jordan Henderson after the midfielder was forced off in their Europa League quarterfinal draw at Borussia Dortmund. (Liverpool F.C. Draw With 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 quarterfinal at Anfield next Thursday.