Rooney has not stayed with the team at the Lowry Hotel in Manchester, as is usual for players in the match day squad before matches.
The rumour is that he will either not feature for United tomorrow, or that he faces a late fitness test before the match to be sure that he can or cannot play. It is possible that the rumour of the fitness test is a ruse to keep Liverpool guessing.
Should Rooney be out, United have few options. James Wilson has not yet been sent on loan as expected, and so remains available for selection. He is, however, inexperienced. Memphis is likely to be used on the left wing, and Anthony Martial is unlikely to be asked to make his debut as a striker against Liverpool, though it is possible he will feature. Marouane Fellaini is another option, and one that Louis van Gaal has previously described him as a number nine for this season.