The absence of Nunez will definitely be felt, I think Firminho will have to come in to replace Nunez. Liverpool have a stronger attack that can penetrate United's shaky defense. Harry Maguire and Martinez will have to work so much and be on their heals through out the 90mins of the game. I hope Manchester United can get a point from the game to boost their confidence for the next round of the competition.
Yes, Firminho will replace Nunez. I think there will be no problem with Liverpool attacking. I even think that Firminho is still better than Nunez since he already played with Liverpool for a longer time. Firminho can play more solidly as a Liverpool attacker, he knows Liverpool play of style better because he already played with the same teammates in many matches.