The club have triggered an option to extend former captain Harry Maguire's contract by a year until 2026.
And United will be able to welcome back skipper Bruno Fernandes at Anfield after he was suspended for Monday's dismal 2-0 defeat to Newcastle.
Defender Maguire, 31, joined the club from Leicester in 2019 and his deal was set to expire at the end of the season.
"I spoke with him (Maguire) this morning and I told him he has to improve on the pitch, we need him a lot," Amorim said on Friday.
"Also, he has to improve as a leader. We all know the situation that he had here (losing the captaincy and falling down the pecking order) but we need him a lot in this moment, so we are going to trigger, happily, the option for him."
Amorim added: "When you look at our team we are starving for leaders on the pitch. He is a leader."
United have lost four consecutive games to tumble to 14th in the Premier League and are out of the League Cup.
The two most successful clubs in English football history could not be heading into Sunday's match in more contrasting fashion.
Liverpool are six points clear at the top of the table, with a game in hand over second-placed Arsenal, and are closing in on United's record of 20 English top-flight titles.
United last won at Anfield nine years ago and have suffered 4-0 and 7-0 thrashings in two of their past three visits.
Amorim, though, is hoping that some rare time on the training pitch this week will help his team.
"In football, in one game anything can happen," he said. "If you talk about the season, then almost every time the best team wins.
"In the moment they are better than us but we can win any game. We have to focus not on the context but the performance. We have to improve the simple things.
"Of course, it is a difficult moment because we are losing too many matches and we are going to be facing the best team of this year, but, like I said, with training, we prepare more the team and we want to improve the performance compared to the last game."
Amad Diallo has been United's one source of optimism during a tough first two months of Amorim's reign.
The Ivorian is close to agreeing a new long-term deal at Old Trafford according to the Portuguese coach.
Marcus Rashford, however, is ruled out once more, this time due to illness.
The England international returned to Amorim's squad for the first time in five games against Newcastle, but was an unused substitute.
