Spurs’ 3-0 win at Old Trafford on Monday (Aug 27) was the heaviest home defeat of his coaching career and the team looked a long way from being realistic title challengers.
So should United bite the bullet and fire the Portuguese coach or give Mourinho time to try and turn things around?
Now in his third season at Old Trafford, United might have already seen the best Mourinho has to offer.
In two spells at Chelsea and at Porto, Inter Milan and Real Madrid he always won the league in his second campaign. However, his third seasons at Chelsea and Madrid ended acrimoniously.
Mourinho won the League Cup and Europa League in his first season at United and finished second in the Premier League last season – albeit a record 19 points behind Manchester City.
But there is little evidence from an illustrious career of an ability to turn things around once the going gets tough.
Mourinho’s relationship with key players appears fractured. There have been high-profile tensions with World Cup star Paul Pogba and his French compatriot Anthony Martial.
The Portuguese has always been a results-driven manager, able to point to a trophy-laden CV, and not feeling an overriding responsibility to enthral his fan base with entertaining football.
That approach caused friction at United even when results were positive in his first two seasons as it did not fit with the attacking traditions of the club under Alex Ferguson and Matt Busby.
Across town, Pep Guardiola has served up some spectacular football at Manchester City and Jurgen Klopp has produced a thrilling attacking side at Liverpool.
But the more prosaic Mourinho now does not even have results to fall back on.
United already trail Liverpool, Spurs and Chelsea by six points and City by four. Unless swift action is taken they risk missing out on the top four and the Champions League next season, while a title challenge already looks unlikely.
Mourinho is not the only figure to blame at Old Trafford, where the team have not won the Premier League since Ferguson’s last season in 2012-13.
Last season’s second-place finish was United’s highest league position in the past five years and many of the club’s fans have laid the blame for the relative under-achievement at the door of executive vice-chairman Ed Woodward.
Fans were hoping the team could push on and mount a serious challenge to City but Woodward did not deliver the centre-back Mourinho wanted in the transfer window despite booming revenues.
Woodward handed Mourinho a new contract until 2020 as recently as January and oversaw the failed reigns of David Moyes and Louis van Gaal before the Portuguese arrived.
“Woodward gave him a contract last season, only seven or eight months ago, and he should see that contract through to the end and do the job,” said former United captain Gary Neville.
But luck does not appear to be on the manager’s side.
Mourinho summoned a positive response to the team’s defeat at Brighton during a dominant first-half display against Spurs that saw Romelu Lukaku miss a gilt-edged chance before the visitors took control after the break.
If the club opt to dispense with his services there is not an abundance of candidates to take his place – with Guardiola, Klopp and Mauricio Pochettino all tied up elsewhere.
As Mourinho defiantly said himself, he has more Premier League titles than the other 19 managers in England’s top flight put together.