Although the club captain struck a positive note as he waved and applauded the fans as he headed down the tunnel, his role as the team's driving force is under serious threat after United thrived with Juan Mata filling his position superbly.
With Ander Herrera also preferred to Marouane Fellaini in the centre of midfield alongside Paul Pogba, Mourinho's side looked more like the vintage United who regularly trampled their opponents at Old Trafford under manager Alex Ferguson.
Superb link-up play as well as rapid and unpredictable ball movement, rarely seen since Ferguson's retirement in 2013, brought the winners of a record 20 league titles an almost surreal 4-0 halftime lead given their recent struggles.
Never quite as gifted as his former team mate Cristiano Ronaldo or United's latest five-star acquisition Zlatan Ibrahimovic, Rooney once dictated games largely thanks to his tremendous work rate and aggression.
But with his pace diminished, Rooney seems to have reached an impasse, being neither an out-and-out striker nor a midfielder.
Attempts to use him as a forward playing behind a target man have also been ineffective as his ability to turn quickly and run behind defenders has decreased.
Mourinho is notorious for his ruthlessness towards big names when they stop delivering and with the pressure on the Portuguese to bring major trophies back to Old Trafford, he is likely to stick to whatever works on the pitch.
The free-flowing football which blew Leicester away will give him plenty of food for thought.
(Editing by Ed Osmond)
