At first glance the game represents the classic FA Cup dream - the minor league team taking on mighty United, winners of the world's oldest cup competition a record 11 times, at a great stadium in front of live TV cameras with a peak evening viewing figure that will run into the millions.
Crawley are the first minor league team to make the fifth round since 1994 and, unlikely though it might be, they are bidding to be the first into the quarter-finals for 97 years.
Progress, however, is not Crawley's aim as they have already landed the juiciest of plums and they will make getting on for a million pounds from the match.
Those are funds that would have been unthinkable in the 1990s and early 2000s when Crawley were in and out of administration and within a whisker of going out of business altogether while bobbing along in the Southern League.
However, things are very different now for the club based in the shadow of Gatwick Airport in southern England.
Not only are all the players full-time but the club has, by minor league standards, bottomless pockets and are well placed for promotion to the Football League for the first time.
FA Cup-loving neutrals the world over will be urging Crawley to do pull off the greatest shock of all but there will also be large proportion of fans of England's minor league clubs hoping they come spectacularly unstuck.
Jealousy at their funding plays a part but much of the ire is directed at manager Steve Evans, who was convicted of tax evasion and fined and suspended by the FA after a contract irregularity investigation during his time as manager of Boston United - issues that contributed to that club also coming close to liquidation.
FURTHER SUBSTANCE
Crawley's status as the Millwall of the Conference - "no-one likes us, we don't care" -- gained further substance this week with when one of their fans was arrested for posting an abusive song about the 1958 Munich disaster, forcing the club to issue an apology.
All that will matter not a jot to the players, however, when they achieve their dream of walking out at Old Trafford to face the most famous team in the land.
"We've beaten three League sides (Swindon Town, Derby County and Torquay United) already and the club deserves a great tie," said Crawley physio Mark Stein, who lost 4-0 to United when playing for Chelsea in the 1994 final.
"To be honest it's unbelievable, it just gets better and better. Hopefully now we can go there and do alright.
It is not just Crawley flying the flag for Sussex, hardly a traditional hotbed of the English game, as Brighton are also enjoying a run of giant-killing and wins over Watford and Portsmouth have earned the League One club a trip to Premier League Stoke City.
Holders Chelsea, bidding to become the first club since Blackburn Rovers in the 1880s to win the cup three seasons in a row, are also in action on Saturday but in a fourth-round replay with Everton following a 1-1 draw at Goodison Park.
