He's clearly unhappy with his options in that position as Mourinho's sides have traditionally had a big powerful DM. Schneiderlin seems like he's another example of a midtable player unable to make the step up to a big club, and Carrick's legs have completely gone (Which begs the question why was he given another contract?).
One of them simply has to start though because a Pogba & Herrera midfield two is just asking for a heavy defeat. We've been far too open against teams like Watford and Stoke, never mind a free flowing Liverpool team who can't stop scoring.
Our record at Anfield isn't great and i'd happily take a draw - not that that's likely to happen as United v Liverpool rarely ends in a draw. There hasn't been one in the league for years.