Just once has Mourinho made it into a fourth campaign, only to leave Chelsea before Christmas during his first spell at Stamford Bridge.

The 55-year-old is now entering his third season as Manchester United manager, but is already being touted as the next Premier League boss to leave his job.

So what leads to Mourinho heading for the exit after season three? And do his sides actually perform worse than the previous two campaigns? BBC Sport examines the evidence.

Built for short-term success?

Having begun his managerial career with a short stint at Benfica, Mourinho enjoyed a successful half-season with Uniao de Leiria that led to Porto appointing the then 39-year-old in January 2002.

Porto:

• 2001-02: Climbed from fifth in the league to finish third after taking over in January
• 2002-03: Primeira Liga champions, Uefa Cup winners, Portuguese Cup winners
• 2003-04: Primeira Liga champions, Champions League winners, Portuguese Super Cup winners, joins Chelsea

Chelsea:

• 2004-05: Premier League champions, League Cup winners, Champions League semi-finalists
• 2005-06: Premier League champions, Community Shield winners
• 2006-07: Premier League runners-up, FA Cup winners, League Cup winners, Champions League semi-finalists
• 2007-08: Leaves club by mutual consent in September

Inter Milan:

• 2008-09: Serie A champions, Supercoppa Italiana winners
• 2009-10: Serie A champions, Champions League winners, Coppa Italia winners, joins Real Madrid

Real Madrid:

• 2010-11: Copa del Rey champions, La Liga runners-up, Champions League semi-finalists
• 2011-12: La Liga champions, Champions League semi-finalists
• 2012-13: Supercopa de Espana winners, Champions League semi-finalists, Copa del Rey runners-up. Leaves Real by mutual consent

Chelsea:

• 2013-14: Third in Premier League, Champions League semi-finalists
• 2014-15: Premier League champions, League Cup winners
• 2015-16: Leaves Chelsea in December

Manchester United:

• 2016-17: Europa League champions, League Cup winners, sixth in Premier League
• 2017-18: Premier League runners-up, FA Cup runners-up
• 2018-19: ?

Mourinho won the title in his first two seasons at Chelsea

The form book

What happens in season three?

Leaving Porto on a high: Two-and-a-half seasons after taking charge, Mourinho left Porto after delivering the Champions League as part of a remarkable treble.

The end at Chelsea, part one: Having won both domestic cups and finished second in the league in his third season, the Blues' fourth campaign under the Portuguese manager got off to a stuttering start and a 1-1 draw at home to Rosenberg in the Champions League saw the reign of the 'Special One' come to an end.

Inter: Mourinho left after two seasons.

Runners-up at Real Madrid: With two games left of the season, it was announced Mourinho would leave Real Madrid. At the time, his side trailed Barcelona by 13 points and had lost the Spanish Cup final to Atletico Madrid, as well as being knocked out of the Champions League at the semi-final stage.

Chelsea, part two: Sixteen league games, just four wins and languishing one point above the relegation zone - Mourinho's tenure was up at Chelsea for a second time, just seven months after he had delivered them a title.

What are the early signs during Mourinho's third season at Manchester United?

Defeat at Brighton on Sunday, following an unconvincing win over Leicester at Old Trafford on the opening day, has done little to dispel the notion of a 'third-season syndrome'.

They host Tottenham at Old Trafford next.

Friction and fallouts - who's to blame?

Mourinho fell out with Real Madrid players after dropping goalkeeper Iker Casillas

Mourinho's departures from both Chelsea, twice, and Real Madrid have followed high-profile fallouts and fractious relationships with both club officials and players.

Do things always come to a head for Mourinho during his third season?

Leaving Porto on a high: Mourinho's knee slide at Old Trafford as his side knocked out Manchester United in the Champions League may have irked Sir Alex Ferguson, but there were no complaints in Porto as he left the club a hero.

Tension at Chelsea: Mourinho's relationship with Blues owner Roman Abramovich became increasingly strained and was not helped when the Russian billionaire bought Andriy Shevchenko for £30m from AC Milan - a player the manager was reluctant to pick.

Tensions bubbled in the January of Mourinho's third season, when he was reportedly unhappy over having a lack of funds to sign players. The pair also disagreed over the arrival of director of football Avram Grant in the summer, who then replaced Mourinho as manager in September.

Winning at Inter: Mourinho didn't make it to a third season at Inter, announcing after the Champions League victory he was "sad, as almost for sure it's my last game with Inter", and adding "if you don't coach Real Madrid then you will always have a gap in your career".

Boiling over at the Bernabeu: "Nobody's been sacked," said Real Madrid president Florentino Perez when announcing Mourinho would leave the Bernabeu, but the announcement followed a string of public arguments with some of the club's key players:

• Mourinho drops iconic goalkeeper and club captain Iker Casillas, who alongside defender Sergio Ramos is then forced to issue a statement denying they threatened to be transferred if the manager was not sacked.
• Portugal defender Pepe says he regrets the handling of Casillas, with Mourinho responding by saying the player's problem was "Raphael Varane" - a rival for Pepe's place in the team.
• Club chairman Perez calls a news conference to address the reports, also denying rumours of in-fighting between Mourinho and club directors.

Feeling blue, again: The Blues' medics felt the wrath of Mourinho in his last season at Stamford Bridge. The Portuguese called them "impulsive and naive" for running on to treat Eden Hazard during a draw against Swansea. Eva Carneiro and Jon Fearn saw their positions downgraded.

Carneiro left the club in the September, eventually settling a dismissal claim against the club the following year.

Then, after a defeat by Leicester City that would prove his last game in charge, Mourinho called out his players.

• "I'm frustrated with the difference between what they do in training and what they do in matches. I don't think in this moment they can feel they are top players or they can feel they are superstars."

Carneiro (centre) settled a dismissal claim against Chelsea and also reached a discrimination settlement against Mourinho

Same again for Jose?

Will Mourinho's third season at Old Trafford be marred by similar disagreements?

A tetchy news conference following a 4-1 pre-season defeat by Liverpool suggested Mourinho was far from happy before the season had even began. Back then, he said:

• If he was a fan, he would not have paid to watch the teams, adding "this is not even 30% of my squad".
• The match "gave me nothing at all" and he was trying to avoid "ugly defeats".
• Antonio Valencia had "too much holiday" and returned in poor condition.

More recently, Mourinho tried to quash reports of Paul Pogba being unhappy.

• Paul Pogba, 12 August 2018: "If you're not happy, you cannot give your best. There are things I cannot say otherwise I will get fined."
• Jose Mourinho, 17 August: "I cannot demand more from him, I cannot ask more from him. I've never been so happy with him as I am now."

But Mourinho was also frustrated by United's lack of activity in the transfer window, saying his side are in for a "difficult season".

The question is, will he be in charge come the end of it?

The counter-argument...

Bar his second spell at Chelsea, when he departed before Christmas, Mourinho has delivered silverware in each of the third seasons he has had at a club.

At Porto this was a treble that put the charismatic Portuguese boss on the map, while during his first spell at Chelsea Mourinho's side won both domestic cups and at Real Madrid he won the Spanish Super Cup in his final season.

But what would be deemed a season of success for many sides is regarded as a minimum requirement at the calibre of clubs Mourinho manages.

He set the bar high at Chelsea, winning back-to-back Premier League titles, but was unable to deliver the Champions League title Blues owner Abramovich so craved.

The Portuguese also failed to achieve European success at Real Madrid, while finishing adrift of Barcelona in the La Liga and lost in the Copa del Rey final to rivals Atletico Madrid before his departure.

There's a fine line between third-season success and third-season 'syndrome', it seems.