0236 GMT May 22, 2019
Mourinho is at the front of the firing line, with odds on him being the first Premier League manager to lose his job this season being slashed after two consecutive defeats, AFP wrote.
However, the Portuguese is far from the only culprit, with United's slide on the field dating back to Alex Ferguson's retirement in 2013.
Here are the three things that have gone wrong for the 20-time English champion.
Not so special anymore
Mourinho introduced himself to English football as ‘the special one’ when taking charge of Chelsea for the first time 14 years ago.
He backed up that bravado by delivering back-to-back Premier League titles. Mourinho's aura and tactical discipline also inspired a title win in his second spell at Stamford Bridge and a treble at Inter Milan. When at the helm at Real Madrid he broke Barcelona's La Liga hegemony under Pep Guardiola.
Yet, his third seasons second time round at Chelsea and at Madrid ended acrimoniously and a third campaign at United already looks as though it is heading the same way.
In contrast to the exciting brand of football offered by Manchester City, Liverpool, Tottenham and Chelsea under Guardiola, Jurgen Klopp, Mauricio Pochettino and Maurizio Sarri, Mourinho's conservative tactics seem outdated and at odds with United's tradition under Ferguson.
Moreover, whereas Mourinho used to staunchly defend his players, at United he has routinely criticized his squad in public.
Spurs fans goaded Mourinho with cries of ‘You're not special anymore’ and his rant at the media as he stormed out of his post-match press conference demanding respect for his record of winning three Premier League titles did little to quell the feeling he is living off past glories.
United only in name
Mourinho's sour mood has not been reserved just for his players, but also the club's executive vice-chairman Ed Woodward over a perceived lack of backing in the transfer window.
Woodward decided there was not value in the market for a host of center-back targets identified by Mourinho and questioned whether they were any better than the five already in United's squad.
It effectively means a former banker is overruling an experienced manager on football matters and United is investigating the possibility of appointing a director of football as a middle man for the first time.
Woodward also insisted neither Paul Pogba nor Anthony Martial were for sale despite a troubled relationship between the manager and both players.
Pogba, who cost United a then world record £89 million ($115 million) in 2016, claimed he would be fined for revealing his true feelings after the first game of the season as his agent Mino Raiola appears to be agitating for a move, with Barcelona apparently interested.
Martial was fined by Mourinho for not returning to the club's preseason tour of the US after the birth of his second child and did not even make the bench for Monday's defeat.
Woodward has been accused of having divided loyalties after United's share price hit a record high last week despite the club's on-field troubles.
Yet, while American owner the Glazer family remains unpopular among many fans, United has spent lavishly in the transfer market in recent years.
The problem is a reported £700 million investment in transfer fees alone since Ferguson retired has been largely wasted.
Big-money signings Angel di Maria, Memphis Depay, Bastian Schweinsteiger, Morgan Schneiderlin and Henrikh Mkhitaryan are no longer with the club.
Luke Shaw, Juan Mata, Martial, Pogba and Alexis Sanchez have also failed to hit the standards they showed at previous clubs to spark United's interest in the first place.
After the match, Shaw said he believes Manchester United's dressing room boasts the spirit and talent to bounce back from Monday's damaging home defeat by Tottenham.
"You always see a lot of things in the media that go on about what our dressing room is like," the 23-year-old told MUTV.
"But, look, we have a really good spirit, a really good group of lads and a group that want to work, want to achieve big things here."
Shaw believes United should have won the game by halftime but, ultimately, defensive and mental brittleness saw Mourinho's men collapse, with just 133 seconds between the visitor’s first and second goals.
"We'll improve, we'll keep working hard. It's early in the season so we've got a lot of games to come and a lot of positive things from tonight."
Pogba said Manchester United's players were in ‘shock’ after their 3-0 defeat to Spurs dealt a heavy blow to their Premier League title ambitions.
"It's bizarre," said Pogba. "(Against Tottenham) we were determined, we started well, and in the end we lost 3-0. It's a shock."
"Even we don't understand what happened," added the French World Cup winner. "We started the game really well, we conceded two goals in the second half.
"The first goal was a real blow, we didn't understand why, because we had the game in hand. One goal, two... we kept pushing, we had chances, and we conceded the third.
"The fans kept pushing us, they were really behind us. We feel really sorry for them, very disappointed. We wanted to do better."