But it is not just the manager's relationship with United's players that has come under inspection, considering he was irked by executive vice-chairman Ed Woodward failing to strengthen the squad before the transfer deadline.
The "Red Devils" were in front inside three minutes, having won a penalty after 75 seconds, and they looked nothing like the side that limped home last season.
It lead the Portuguese to vent his feelings after the final whistle at Old Trafford and reiterate his warning for the new season.
"I'll always give my best to the fans and my teammates no matter what's going on", he wrote, along with #pogfeelings. "I had my plans for many months and I find myself with the market closed in a situation I did not think I would be in". Football managers should be called now more head coaches. "We thought he would manage maximum 60 minutes and he went much longer", Mourinho said. I think his reaction showed what it meant to him. If you have round pegs in round holes, and all of them are doing the right job at the same time, then you are going to do well.
Leicester will hope to get their first points on the board when they welcome Premier League new-boys Wolves to the King Power Stadium next Saturday.
But in comments attributed to Pogba in today's British newspapers, he says: "There are things I can say and there are things I cannot say. otherwise I will get fined".
The former Juventus midfielder who opened scoring in the third minute from the penalty spot said he was playing for those who trusted his game.
"Pogba was a monster", said Mourinho.
"Paul was fantastic, his contribution was unbelievable but the fuel was disappearing".
Mourinho made a decision to name Pogba as captain in the absence of Antonio Valencia as United try to convince the 25-year-old midfielder that his long-term future lies at Old Trafford. Maybe in the next game I can give to Alexis.
Their best chance for a stretch came when skipper Pogba threaded through Sanchez, whose laid off for Juan Mata to get away a shot that was deflected just wide.
Mourinho's first change against Claude Puel's men saw him replace Marcus Rashford with Romelu Lukaku, while he introduced Fellaini and McTominay to shore things up in the midfield.