The game will be played in the first weekend of January, just a week after United head to Deepdale for a Championship fixture.
Scunthorpe have already beaten the Lilywhites once this season, registering a 1-0 win at Glanford Park in sss.
"We're really pleased, we've already beaten them once this season," Iron boss Nigel Adkins told BBC Radio Humberside.
"We go and play them on Boxing Day, then we'll look forward to that game and be as positive as we can."