Six wins from seven and joint top of the Premier League, the Red Devils have cruised thus far but haven't been truly tested.
Victory at Anfield would dispel any doubts of their title credentials and potentially end Liverpool's hopes of being a contender.
Fans were eager to see what Jurgen Klopp and Jose Mourinho's teams would look like following the international break and now they've been revealed.
Here's how the two teams will line up:
Simon Mignolet; Joe Gomez, Joel Matip, Dejan Lovren, Alberto Moreno; Georginio Wijnaldum, Jordan Henderson, Emre Can; Philippe Coutinho, Mohamed Salah, Roberto Firmino.
David de Gea; Ashley Young, Antonio Valencia, Phil Jones, Chris Smalling, Matteo Darmian; Ander Herrera, Nemanja Matic; Henrikh Mkhitaryan, Anthony Martial, Romelu Lukaku.
Both very strong sides, but there was cause for concern amongst United fans when their starting line-up was announced.
Mourinho appears to have chosen a 3-5-2 formation which will feature Valencia in a back three with Young and Darmian in the wing-back positions.
So where on earth is Eric Bailly? No one knew at the time.
The Ivorian has been solid at centre-back this season and played a vital role in United conceding just two goals all season.
Well, the reason for Bailly's mysterious absence has now been revealed by United themselves on their official Twitter account.
Bailly apparently suffered an injury while on international duty and can't play as a result. Marcus Rashford is also unavailable for the same reason (see below).
The tweet said: "Eric Bailly sustained an injury while on international duty, and Marcus Rashford picked up a knock with England."
United fans will only hope it's nothing serious.