It's actually happened.
Claudio Ranieri has moulded together a team of free transfers, lower league imports and journeyman players and turned 5,000/1 outsiders into a top flight title-winning team.
Among them are a former United triallist (Jeff Schlupp) and former Reds Academy products Danny Drinkwater and Danny Simpson.
How could those three have imagined that - having been rejected and released from Old Trafford - they would go on to star in the greatest underdog fairytale of them all:
Leicester City's Premier League title triumph.
Usually, when players leave United it's seen as a backward step in their careers but for Schlupp, Drinkwater and Simpson it's proved the exact opposite.
After brief and largely unfulfilling periods at the club, the future looked bleak but now they've all achieved something many would have said was more likely had they stayed and developed at United: a Premier League winners medal.
Drinkwater, who was recently capped by England, never played for the United senior side.
He was a regular in the club's youth and Reserve sides in the late 00s and made the first team bench for a match at Hull in 2009 but was then loaned out, never to return.
Schlupp never even made it as far as any of United's teams.
The left-sided player was on trial at Old Trafford during the 2012/13 season, Sir Alex's last as manager, before he returned to Leicester and moved through the ranks into the first team.
Schlupp says he has "no regrets" about his rejection and that he would return to United if given the chance, but he has instead become an integral part of the Foxes unlikely successes.
Right-back Simpson was at Old Trafford for five years and, unlike his team-mates Schlupp and Drinkwater, broke into the senior side under Sir Alex.
Simpson was picked up by United in 2003 and rose through the ranks into the reserve set up in 2005 and then made his first team bow two season later.
That came in 2-0 League Cup loss against Coventry and a league debut quickly followed on 6 October 2007 in a 4-0 home win over Wigan, with Simpson setting up the fourth goal for Wayne Rooney.
Two further first team appearances followed - both in Europe against Dynamo Kyiv - before the return to fitness of Wes Brown and Gary Neville prompted Simpson's loan move to Ipswich.
Newcastle, Blackburn and QPR followed before the full-back joined Leicester for the start of last season, a chain of events that set in motion one of sport's most romantic and unlikely stories.
Unlikely lads. Simpson, Drinkwater and Schlupp learned their trade at United and have now become champions with Leicester City.