Manager Juergen Klopp said Monday the forward sustained a concussion in the 3-2 win over Newcastle in the Premier League on Saturday and "would not even be allowed to play" by team doctors.
Salah "feels OK but it's not good enough from a medical point of view," Klopp said at a news conference. "He's desperate (to play). But we cannot do it."
Salah's head hit the ground hard after he collided with Newcastle goalkeeper Martin Dubravka, who came out to punch away a cross. He had earlier scored his league-leading 22nd goal of the season.
Klopp suggested Salah will be fit to face Wolverhampton Wanderers on Sunday at Anfield in the team's decisive final Premier League game.
Against Barcelona, Liverpool is also trying to overcome a 3-0 first-leg deficit without forward Robert Firmino, who has a muscle injury.
"Two of the world's best strikers are not available," Klopp said, noting his team likely needed to score at least four goals to advance to the final.
Firmino was replaced by Daniel Sturridge in the starting lineup against Newcastle, while substitute Divock Origi came on for Salah to score a late winning goal.
"It looks you have to be perfect to beat (Barcelona) and we should try that," Klopp said, adding his players could "fail in the most beautiful way. Celebrate the situation with good football. It should be a football party."