Salah, Liverpool's leading scorer in all competitions this season, sustained a head injury in the Reds' 3-2 victory over Newcastle United on Saturday.
The Egypt forward had to be taken off on a stretcher in the 73rd minute, with his replacement Divock Origi scoring the winner 13 minutes later.
Speaking ahead of Barca's trip to Anfield, Klopp confirmed Salah had suffered a concussion but will be fit for Sunday's decisive final-day Premier League clash against Wolves.
Firmino, meanwhile, missed the Newcastle clash with an ongoing groin problem, and will remain on the sidelines as Liverpool look to overturn a 3-0 deficit.
"Both are not available for tomorrow," Klopp told a news conference.
"[With Salah] it's concussion so he wouldn't be allowed to play. That's it.
"He feels okay, but it is not good enough from a medical point of view. That's all. He's desperate [to play in] everything, but we cannot do it."
— Liverpool FC (@LFC) May 6, 2019
When asked if Salah will be available for the weekend, Klopp replied: "Yes."
Luis Suarez and Lionel Messi put Barca in control of the tie at Camp Nou on Wednesday, with Salah hitting the post late on.
Liverpool responded with a hard-fought 3-2 win at St. James' Park, moving back to the top of the Premier League, with Manchester City hosting Leicester City on Monday.
It was a result that means the title will be decided on the final day of the season, when City travel to Brighton and Hove Albion as Liverpool take on Wolves at Anfield.
Photo Getty Images. Caption: Liverpool forward Mohamed Salah