Liverpool will be without top scorer Mohamed Salah for Tuesday's semi-final, second leg after manager Jurgen Klopp revealed he was concussed in a 3-2 win at Newcastle.
The Egyptian was stretchered off at St James' Park on Saturday due to a head knock sustained as he challenged Newcastle goalkeeper Martin Dubravka for a high ball.
"It's a concussion so that means he would not even be allowed to play. So that's it," said Klopp at his pre-match press conference on Monday.
"He feels OK but it is not good enough from a medical point of view that is all. He's desperate (to play) everything but we cannot do it."
Klopp will also be without Brazilian striker Roberto Firmino due to a groin injury.
"Two of the world's best strikers are not available tomorrow night and we have to score four goals against Barcelona to go through after 90 minutes," added Klopp.
"It doesn't make life easier, but as long as we have 11 players on the pitch, we will try it."