Liverpool manager Rafa Benitez has confirmed that Steven Gerrard will undergo a scan on the injury sustained in the 1-0 FA Cup fourth-round replay loss to Everton.
Reds captain Gerrard was replaced by Yossi Benayoun on 16 minutes at Goodison Park after picking up a hamstring problem. His side were dealt a further blow when Lucas Leiva was handed a second yellow card 14 minutes from time.
The Toffees then left it late to secure victory as teenager Dan Gosling netted in the dying stages of extra-time to set up a fifth-round tie with Premier League rivals Aston Villa.
"I don't know how long Steven will be out for," Benitez told the club's official website.
"He was injured and he asked to come off. He will have a scan on Thursday and we will have to wait and see.
"I am really disappointed to have gone out of the FA Cup. To play for a long time with 10 players and then to concede a goal right at the end from a deflection, we have to be disappointed.
"The turning point of the game was the sending-off but I prefer not to say anything about that.
"You can lose players which is part of the game but when you play with 10 players and they are working as hard as they did tonight it was really bad luck at the end."
The Spaniard continued: "We now have to concentrate on the Premier League and the Champions League so there is still a lot to play for.
"They are two massive competitions and we are in a very good position."
Benitez also defended his decision to substitute Fernando Torres for Ryan Babel in extra-time, adding: "Torres was really tired and that's why I took him off.
"He needs to keep playing games and keep training because his match fitness is not the best but that will come."