After three losses in a week, Mourinho's previously undefeated start to his managerial career at Manchester United has unraveled.
Following a disastrous end to his time at Chelsea that culminated in his sacking in December 2015, questions are being asked about the Portuguese's ability to restore United to its former glories.
Having spent £145 million ($190 million) on new signings during the recent transfer window, many believed Mourinho had assembled a team capable of winning the Premier League after the club's disappointing fifth-place finish in the 2015-16 season.
Confirmed as the replacement for departing United manager Louis van Gaal in May, Mourinho's Old Trafford tenure began in encouraging fashion.
United claimed the Community Shield with victory over Leicester City and recorded league wins over Bournemouth, Southampton and Hull City. Four wins from four -- with new striker Zlatan Ibrahimovic adapting well to the demands of English football -- and things were looking rosy.
But a solid start has been derailed by three defeats in a row. Back-to-back league losses to Watford
and local rivals Manchester City
came either side of a 1-0 loss to Dutch side Feyenoord
in the Europa League.
Against Watford, Mourinho suggested that his players were struggling with the pressure of playing for one of the world's biggest teams he and singled out defender Luke Shaw for specific criticism.
Refereeing decisions have also played a part in United's recent defeats, according to Mourinho, who highlighted what he thought was a foul on Anthony Martial before Watford's first goal, a potential offside in the build-up to Feyenoord's goal, and being denied a penalty in the Manchester derby.
"The referee's mistakes are not in my control, there is nothing I can do about that," said Mourinho. "We were punished by these mistakes and I can't do anything about it."
The Red Devils have now slipped to seventh in the Premier League on nine points, six points behind early leaders City. This is the first time Mourinho has suffered three successive defeats since managing FC Porto in 2002.
However, it is not just the short-term run of results that will be a concern for United fans. If you examine Mourinho's final days at Chelsea, the stats are even worse.
His Chelsea side managed just eight points from the 10 games before his sacking having won the Premier League title in the previous season.
They lost nine of the 16 league games that the Portuguese took charge of in 2015-16 and sat in 16th place when he departed.
Since the start of that season, Mourinho has won just one third of the games he has taken charge of, some way below the 65.4% win record across the whole of his managerial career.
This amounts to 24 points from his last 22 league games. In contrast, Mourinho's title-winning Chelsea side accrued the same number of points in just 11 games at the end of the 2014-15 season.
In the league, Man United next face defending league champions Leicester, which has won three of its past four games, scoring nine goals in the process. With one side struggling for form and the other starting to find some, it will be an intriguing encounter.
Before that on Wednesday, though, there is a potentially tricky away game for United against lower league Northampton in the EFL Cup.
In 1970 the two sides met in a FA Cup match, with United great George Best scoring six goals in a 8-2 win.
But if United were to lose on Wednesday, the knives could really be out for Mourinho.