Brazilian Firmino has a muscular injury and was not included in the squad for Saturday's game at St James' Park.
"They both are not available for tomorrow," Klopp told a news conference.
"Two of the world's best strikers are not available and we have to score four goals to go through in 90 minutes.
"It doesn't make life easier but as long as we have 11 players on the pitch we will try... if we can do it wonderful and if not, fail in the most beautiful way."
Salah is expected to feature against Wolverhampton Wanderers in Liverpool's final Premier League game of the season on Sunday but Klopp said the clash with Barcelona was too soon for the 26-year-old.
"It's a concussion for Mo. He would not be allowed to play. He feels Ok but it's not good enough from a medical point of view. He's desperate but we cannot do it," Klopp added.
"Together with our supporters this was a long season and there's a little chance to make it even longer. If not, these are the last two home games of an incredible season.
"We should celebrate it with a good performance on the pitch and in the stands."
Defender Trent Alexander-Arnold said Liverpool would have to be fearless to have a chance of progressing.
"That's the only way we're going to get a result. If we get caught up in fearing their players then that's not really going to work," Alexander-Arnold added.
"We have had decent results this season where we have scored more than three goals and being at home helps us. There's still that sense of belief but we know it's going to be hard. But anything is possible, especially at Anfield."
(Reporting by Shrivathsa Sridhar in Bengaluru, editing by Ed Osmond)
Share
