The embarrassing defeat left Louis van Gaal red-faced, with a lot to consider...
Why on earth did Manchester United not sign any defenders?
So it's taken just two games for the excitement over Radamel Falcao to die down. Indeed, Manchester United's decision not to sign a new defender and simply recruit enough attacking players to outscore the opposition is already backfiring.
There is irony in the fact that Leicester City won 5-3, as many had commented that United's defensive weaknesses won't matter because they will always score one more goal than the other team. Why on earth did Louis van Gaal not demand new defenders?
Defending is a team game
At the same time, it's not so much a case of defensive personnel as the back line not getting enough support from the front.
Defending is a team game. If Man United's starting XI is loaded with top-heavy attacking players, who will press off the ball and track back?
While other teams defend with 11, United defend with five or six at best and that is something they will be forced to address unless they want to concede five regularly.
Di Maria is worth every penny
That said, Angel Di Maria so far looks worth every penny at Old Trafford.
If anyone was worth the money United paid for them this summer, it is Di Maria. It is simply a shame for the Argentine that his team-mates do not look up to scratch at the moment.
Mata's days could be numbered
The 5-3 loss at Leicester was also noteworthy for Juan Mata. The Spaniard scored in United's 4-0 win over Queens Park Rangers but many speculated that his long-term future at the club was at risk in the wake of their summer signings.
And, sure enough, he was left on the bench against Leicester, with the 26-year-old coming on and making a mistake for one of the goals in the second half.
If he isn't careful, Mata's days in Manchester could be numbered.
Back down to Earth with a bang
Last week's win over QPR had people asking whether United could win the league. Why...?
This week, Manchester United were brought back down to Earth with a bang. Being 3-1 up against a newly promoted side, Van Gaal's team simply gave up and let Leicester dominate. Okay, the penalty for the second goal was an incorrect decision. But did Rafael have to brainlessly foul his man? And did United have to then go on to concede three more goals?
Of course not. Van Gaal's side look awful in defence right now - as bad as and maybe even worse than Liverpool. No front line in the world will make up for that.
This season is going to be a long one. Talk of anything more than just about fighting for a top-four spot is a pipe dream.