SEPT 10 — After the unwelcome intrusion of the international break, proper football resumes this weekend as the main European leagues return to action.

And the action could hardly be returning in a more emphatic or dramatic fashion, with the limelight falling squarely upon without doubt the biggest game of the season so far: Manchester United versus Manchester City… otherwise known as Jose Mourinho versus Pep Guardiola.

It’s a mark of how far City have progressed in the last few years that this fixture has become such a major deal.

Until now, for most fans around the world the “one to watch” in the English Premier League was Manchester United against Liverpool. Even though the Merseyside Reds have suffered an ignominious fall from grace in the last couple of decades, there has still always been something special about that particular contest to set it apart from the rest.

Other games have come close: Arsenal or United against Chelsea, for example, or the North London derby between Arsenal and Tottenham, also hold a certain appeal, and there were also several spectacular collisions between Arsenal and United around a decade ago before Arsene Wenger lost the plot.

Manchester City, though? You could take them or leave them, really. Even for United fans, their rivals in the same city, the derby with City was not a particularly important occasion. Sure, they wanted to win for local bragging rights, but they’d much prefer to beat Liverpool, Arsenal or Chelsea instead.

Now, though, not only is City’s trip to Old Trafford this weekend the biggest game of the Premier League season, it is also among the most eagerly anticipated duels in world football, perhaps only eclipsed by Barcelona versus Real Madrid.

The main reason for that, of course, is the managers, and it will certainly be fascinating to see who gets the early upper hand in this renewal of hostilities between bitter adversaries Mourinho and Guardiola.

It is a personal rivalry which first emerged in early 2008, when both men were the front-running candidates for the same job. After much discussion and doubt, Barcelona’s board eventually plumped for Guardiola. The rest is history, and since then they have clashed on many occasions, with both men enjoying triumphs and enduring disasters.

Mourinho, for starters, came out on top with Inter Milan in a famously bad-tempered Champions League semi-final against Guardiola’s Barcelona in 2010, and later won the Spanish league title with Real Madrid in 2012.

Guardiola’s Barca, on the other hand, produced arguably their best-ever performance to destroy Mourinho’s Madrid 5-0 in their first “Clasico” meeting in November 2010, and he also ended up knocking Madrid out of the Champions League later that season en route to their second European title in three years.

So honours are roughly even and now they are not only both in the same league, they are both in the same city, and both will be equally determined to prevail.

Make no mistake, this is a proper rivalry. The level of antipathy between sportsmen is often exaggerated by media marketers in a transparent attempt to whip up a frenzy of excitement, even though the truth is generally more prosaic: professional athletes rarely dislike each other as much as we are led to believe.

But with Mourinho and Guardiola it is different. Ever since the Portuguese was overlooked by Barcelona when they appointed the Spaniard eight years ago, he has been desperate to prove them wrong. I truly believe that all the bad things we sometimes see in Mourinho -- his nastiness, his bitterness, his callous ruthlessness — derives directly from that snub.

Barcelona, the club where Mourinho kick-started his coaching career under Bobby Robson and Louis van Gaal, was his dream club. He was always convinced he would return as manager, and in 2008 he became even more certain that his time was coming.

To be brushed aside for a managerial novice was deeply hurtful to Mourinho, and it has fired him ever since. If beating Barcelona is his biggest motivating passion, then beating Guardiola is his second.

Both men have already achieved so much as managers, but they couldn’t be more dissimilar either as personalities or in terms of their coaching philosophies. The difference, perhaps, could be summarised by saying that Mourinho will do anything to win, whereas Guardiola will do anything to defend his footballing beliefs.

So, what will happen when they go head to head this weekend? Unlike many pundits I am going to be honest and say this: I don’t know.

Guardiola’s insistence that City pressurise United high up the pitch could completely knock Mourinho’s men out of their stride, or the latter’s ability to impose counter-attacking methods could allow the Red Devils to draw their opponents out and then hit them with a killer break.

Neither manager, of course, will actually be on the field of play. And although these two men are capable of influencing the action like few other coaches, the encounter could well be decided by an error or a piece of individual brilliance.

Anything could happen, a tight and tactical goalless draw or a goal-laden thrashing either way or anything in between, but with Mourinho and Guardiola on the sidelines there is one certainty: the world will be watching.

* This is the personal opinion of the columnist.