United streaked into a 3-1 lead at the King Stadium with Van Persie, Angel di Maria and Ander Herrera all finding the back of the net, but the visitors capitulated in the final 30 minutes as the Foxes scored four times without reply to clinch a breathtaking three points.
It was an infuriating and inexplicable collapse from Manchester United and, as Van Persie explains, led to some confrontations in a meeting organised by Louis van Gaal to get to the bottom of the debacle.
"It shouldn't be possible [to lose like we did],” Van Persie, who has scored 48 goals for the club, told Fox Sports News. "But it still happened. We have to deal with it.
"We had a proper look at it next day. Sometimes it was a bit confronting and it was a long meeting. One hour [or] something.
"We went from there, started again this week [and have put] a couple of really good sessions in. Everyone feels ready to face West Ham."
Must win game
Should Manchester United lose again on Saturday, and there is certainly a chance given their defensive concerns, then it is feasible they could be seven points of the Premier League’s coveted top four after only six games played.
This encounter with West Ham does, then, feels like something of a must win game. It was only two weeks ago that United were in this position, searching desperately for three points, and they responded accordingly with a convincing win over Queens Park Rangers.
But this weekend should, on paper at least, present a far more difficult proposition when taking in consideration the issues Manchester United have a back and the recent form that the opposition have been able to produce.
Manchester United enter into the game without a fit out-and-out central defender, with Jonny Evans, Chris Smalling, Phil Jones and Tyler Blackett all unavailable. Marcos Rojo, who has started both his games at left-back, will move into the middle, but the other place is up for grabs.
Meanwhile, only Chelsea, Everton and Arsenal have scored more league goals than West Ham this season, who recorded a very impressive win over Liverpool in their last outing. They will be confident of a result this weekend.