This game was billed as a Top Four play-off with the Foxes needing to win, and United only needing a draw ahead of kick off.
But with Chelsea winning at home to Wolves to secure their place, the second half pressure was too much for the hosts as they slip down into the Europa League spots.
Both sides showed plenty of nerves in the opening stages, with Kelechi Iheanacho’s pot shot the closest either came to a goal.
Marcus Rashford carved out United’s best chance of the first half, but Kasper Schmeichel as he palmed away his long range strike.
With updates from Stamford Bridge beginning to filter through after the break, Leicester looked to push on, as Jamie Vardy was inches away from scoring.
The former England man got the better of Harry Maguire in the air, but with David De Gea glued to the floor, his header came back off the bar.
But despite having the better chances, Leicester were to shoot themselves in the foot with 20 minutes to go.
Jonny Evans rashly fouled Anthony Martial inside the box, and Fernandes showed off his trademark hop skip and goal technique from the spot.
That goal broke Leicester hearts, and the expected onslaught never really arrived, as Evans late red card completed a miserable end to the season.
FULL TIME AT THE KING POWER STADIUM IT’S LEICESTER CITY 0 MANCHESTER UNITED 1