Managers are exposed by the Champions League.

A tournament involving the elite will always test teams to the limits of their competitiveness, and the knockout element of the latter stages inevitably makes some games vulnerable to chance. Even so, it is the grandeur that is the most dangerous aspect to managers. Owners consider winning the Champions League as the pinnacle of achievement, there is a glory that cannot be replicated elsewhere, and managerial careers become victims of their restless ambition to land the trophy.

Despite winning the Barclays Premier League last season, Roberto Mancini cannot be certain of his future at Manchester City. Failing to reach the knockout stages of the Champions League for a second successive campaign is the kind of setback that can undermine even a successful manager. The Italian's record in the competition has been underwhelming, and even retaining the domestic title might not be enough to keep Mancini at the Etihad Stadium. He will be wary, for instance, of the appointments of Ferran Soriano, the former Barcelona vice-president who is now City's chief executive, and Txiki Begiristain, the former Barcelona sporting director who now has a similar role at City.

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Clubs can generally be split into two different cultures – the minority run by exceptionally wealthy individuals who are often impetuous and impatient, and the soberer majority, where the pursuit of glory is understood within a wider perspective. Roman Abramovich falls into the former category, and was heedless of all views but his own when he last month jettisoned Roberto di Matteo.

The Italian had last season delivered the Champions League as interim manager, finally satisfying the oligarch's craving for the trophy. Yet the threat of being knocked out in the group stages this season – Chelsea need to defeat FC Nordsjaelland tonight and hope that Juventus lose at Shakhtar Donetsk – was enough to persuade the Chelsea owner to ditch the manager 13 days ago and replace him with Rafa Benitez, even though the Spaniard is deeply unpopular among the club's fans because he was manager of Liverpool during a time of antipathy between the two clubs.

Mancini and Benitez are haunted by two managers who loom large in the thoughts of their club's owners. Pep Guardiola is coveted by Manchester City and Chelsea, while Jose Mourinho is expected to return to England in the summer and the Etihad Stadium or Stamford Bridge seem his only two likely destinations. Sir Alex Ferguson was last Monday night generous in his praise of Mourinho in an extensive and enlightening television documentary on the Portuguese manager, and declared that he could manage any club in the world. Even if Ferguson did consider him a potential heir at Old Trafford, though, the Scot is unlikely to leave United in the summer.

The pursuit of Mourinho and Guardiola is indicative of the culture of instant success that club benefactors seek to impose. Since the Portuguese manager left Stamford Bridge, stability has never been a guiding principle and Abramovich will always be liable to reach for an abrupt solution. In recent days, Chelsea have denied that Avram Grant is being lined up to return to assist Benitez, who has failed to improve the team's fortunes. Decisiveness is second nature to Abramovich, but the long-term reign of Arsene Wenger at Arsenal is no longer a rebuke since it is seven and a half years since the Frenchman won a trophy.

Even so, Wenger features on a shortlist of three managers to replace Carlo Ancelotti that Paris St Germain are considering. The others are Mourinho and Guardiola. An individual's stock can remain high, and Wenger's husbandry of Arsenal's resources even remains attractive to clubs with limitless wealth. The lure of Mourinho is that he is uncommonly successful. No other manager has won the premier league in England, Italy and Spain, and he is twice a winner of the Champions League, with Porto and Internazionale. With Guardiola, romanticism prevails, since the quality of the football his Barcelona side played was rarefied.

That depiction is not wholly reflective of both managers, since Mourinho's teams will play to their strengths and that can be attractive on the eye, while Guardiola set out to be successful and implemented a style of play at Barcelona that had the purpose of denying opponents the ball rather than achieving a certain beauty. In truth, they are coveted because they are considered the leading managers of their generation – Ferguson apart – and so are in vogue.

There are other factors to consider, and AC Milan have been courting Guardiola while he lives in New York with his family during a year's sabbatical. The Spaniard is expected to make a decision about his future in February, and Stamford Bridge seems an unlikely destination. Manchester City look a better fit for Guardiola, which would leave Mourinho likely to return to Stamford Bridge.

The club owners will always remain impatient, though.