Roberto Firmino left Old Trafford on crutches after suffering an ankle injury in the first half of Liverpool's draw with Man United.
Jurgen Klopp described the Brazilian's injury as a "catastrophe for us" - which could be bad news for Liverpool should he miss any of their upcoming fixtures.
Manchester United were forced to make all three of their substitutions in the first half, whilst Firmino was also taken off to be replaced by Daniel Sturridge.
Liverpool were frustratingly held to just a point, although they regain top spot over title rivals Manchester City.
With clashes against Watford and Everton to come, Firmino's fitness will be a huge concern for Klopp, with Sturridge looking well off the pace against United.
According to the Mail's Dominic King, Firmino did not have his foot in a protective boot, but left on crutches whilst departing Old Trafford.
Image: Getty Images via Liverpool FC
Despite labelling Firmino's injury as a "catastrophe", Klopp said at his post-match press conference: “Unfortunately, I have no clue. It was something with the ankle, that's for sure.
“Bobby said at first he could carry on but then he showed it didn't work.
“I don't know exactly; it is Bobby, so it will be quicker than with all the others but first we have to know what it is exactly – and we don't know at the moment.”
The hope will be it's just a minor strain rather than any ligament damage, which would be a big blow for the Reds.
Dejan Lovren and Joe Gomez are still ruled out, whilst Alex Oxlade-Chamberlain is not yet ready to make an appearance after returning from injury.
Klopp may turn to Divock Origi or Xherdan Shaqiri should the Brazilian be absent for a while, although Sturridge remains the most likely contender.
The club are expected to provide another update on his injury in the coming days.