The Blades travel to Birmingham today (kick-off 3pm) to face Aston Villa at Villa Park and should they snatch a surprise victory or the scores are equal at 90 minutes to force a replay then the S2 club will be in the hat for the fouth round.
The draw for the next round - regardless of whether United make it or not will take place tomorrow on ITV at 2pm.
The numbers in full:
1. Barnsley or Coventry City
2. Yeovil Town or Leyton Orient
3. Liverpool or Oldham Athletic
4. Nottingham Forest or West Ham United
5. Bristol City or Watford
6. Southend United or Millwall
7. Middlesbrough or Hull City
9. Kidderminster Harriers or Peterborough United
10. Doncaster Rovers or Stevenage
11. Stoke City or Leicester City
12. Southampton or Burnley
13. Newcastle United or Cardiff City
14. Rochdale or Leeds United
15. Wigan Athletic or MK Dons
16. Charlton Athletic or Oxford United
17. Manchester United or Swansea City
18. Port Vale or Plymouth Argyle
19. Norwich City or Fulham
20. Aston Villa or Sheffield United
21. Macclesfield Town or Sheffield Wednesday
22. Sunderland or Carlisle United
23. Bolton Wanderers or Blackpool
24. Blackburn Rovers or Manchester City
25. Everton or QPR
26. Brighton & HA or Reading
27. Arsenal or Tottenham Hotspur
28. Birmingham City or Bristol Rovers or Crawley Town
29. Grimsby Town or Huddersfield Town
30. Ipswich Town or Preston NE
31. Derby County or Chelsea
32. AFC Bournemouth or Burton Albion