According to the Red Devils' official website, the trio will miss the trip to Merseyside due to injuries. The France international sustained a hamstring injury in the first Champions League fixture of the season against FC Basel.
Pogba has reportedly returned to light training, but is still nowhere close to making a return from injury. France manager Didier Deschamps is not expecting Pogba to return before the next international break, which starts on 6 November.
Fellaini suffered a knee injury while on international duty with Belgium. He is expected to miss the trip to Liverpool as the former Everton star is set to be out of action for a "couple of weeks" as confirmed by the Belgium FA.
United were without the services of Michael Carrick for their last two games due to injury. The former Tottenham Hotspur man is expected to miss the Red Devils' upcoming clash against Liverpool, says United's official website.
Pogba, Fellaini and Carrick join long-term absentees Zlatan Ibrahimovic and Marcos Rojo on the treatment table and these players will miss United's clash against Liverpool.
The situation leaves Mourinho with Nemanja Matic and Ander Herrera as the only recognised midfielders in the squad. The Portuguese tactician claims there is "no problem" at United because of Fellaini's injury setback.
"From what I read, I don't think he [Fellaini] can play the match. Another one plays and it's no problem for me. Not just Ander. We trust every player. We lost players last season and we lost players this season. With our way of thinking and feeling, it really is no problem," Mourinho explained.
"One player not playing means another one plays. It's an opportunity for another one and we trust them. We never hide behind this or that player or this or that injury. We trust the ones that are going to play."