Salah left the pitch on a stretcher after an aerial collision with Newcastle keeper Martin Dubravka during Saturday's 3-2 win.
Manager Jurgen Klopp says concussion will keep Salah out, as Liverpool look to overhaul a 3-0 deficit at Anfield.
Firmino missed the win over Newcastle with a muscle injury.
"Two of the world's best strikers are not available tomorrow night and we have to score four goals," said Klopp.
"It doesn't make life easier but we will try for 90 minutes to celebrate the Champions League campaign to give it a proper finish."
Defender Virgil van Dijk and midfielder Alex Oxlade-Chamberlain also both missed training on Monday.