With Newcastle having secured their spot in the top four on Monday night, Jurgen Klopp’s side had to hope United would lose both of their remaining games to catch them on the final day.
Liverpool have ended the season strongly but endured a difficult time of things earlier on in the campaign and even a late winning run was not enough to catch up.
A draw with Aston Villa on Saturday all-but ended any lingering hopes it would be possible.
Inconsistent form condemns the Anfield giants to the Europa League for the first time since Klopp led them to the final in 2015/16.
While the Reds boss has stressed his team are “okay” with their fate, Salah vented his frustration on Twitter.
“I’m totally devastated,” he wrote.
“There’s absolutely no excuse for this. We had everything we needed to make it to next year’s Champions League and we failed.
“We are Liverpool and qualifying to the competition is the bare minimum. I am sorry but it’s too soon for an uplifting or optimistic post. We let you and ourselves down.”