The Reds are faced with the unusual situation of having to await the Tranmere Rovers-Watford replay being played only three days before the next round.
Due to the Prenton Park pitch being waterlogged, their tie has been rearranged for a week on Thursday, only two days after Watford face Aston Villa in the Premier League.
The Hornets are already selling tickets to their fans for the United clash, and will refund the money if they are knocked out.
We will provide further updates on our ticket situation but applications for both potential games will open at 08:00 GMT on Monday 20 January and close at 20:00 GMT on Thursday 23 January.