The centre-back role has been the centre of some experimentation in the Premier League

Pep Guardiola and Jurgen Klopp have been chief among those deploying non-traditional defenders

Lucas Leiva, Emre Can, Liverpool

Liverpool's Emre Can and Lucas Leiva. Picture by: PA Wire / PA Wire/Press Association Images

While it was admirable how quickly his players bought into his methods, Pep Guardiola's Manchester City project was always going to hit a hiccup or two early on.

And we may well have arrived at that period, with a 3-3 draw against Celtic in the Champions League followed up by a 2-0 loss to an impressive Tottenham.

It's not time to panic of course because as mentioned already, a "project" - modern managerial parlance for developing a team - takes time to bed in. Indeed, Spurs manager Mauricio Pochettino knows about that and also is benefiting from the fact that this season Tottenham are further along in their own project.

But one thing that City's recent results point to are defensive frailties. And it ties into something Kevin Kilbane noted about Liverpool.

Both sides press, although they do so in different ways. As Kevin pointed out in his Newstalk.com column before the weekend, Liverpool's often unimpressive defenders are not exposed because of the pressing high up the field which reduces the amount of work they have to do.

But as the Leroy Fer goal for Swansea showed on Saturday, when it comes to set-pieces and other key moments for defenders when emphasis is placed on their abilities and cohesion, Liverpool still have weaknesses.

Pep's Barcelona used to press relentlessly in their most successful period. But they also dominated possession which reduced the defensive work-load of the back-four.

Claudio Bravo

Similarly, it seems City will tend to monopolise possession, especially once they get even more accustomed to his message.

And that starts from the back where the goalkeeper Claudio Bravo and centre-back John Stones have been signed more because of what they can do with the ball then what they do when the other team has it.

There is nothing wrong with that at all as that philosophy has underpinned Guardiola's successes. And he is not alone.

From time to time over the years, we have been seeing midfielders or full-backs being reconstructed into centre-backs. It worked with Javier Mascherano at Barcelona, while Aleksander Kolarov hasn't been disastrous in that position on the occasions that Guardiola has moved him in there on occasion at the start of this season.

Even Lucas Leiva, a water-carrier of a defensive midfielder has filled in as s centre-back in a back-four, including in last season's Capital One Cup final. That is slightly more radical than Brendan Rodgers' previous experiment with a back-three featuring Emre Can, who at least has played left full-back previously.

Lucas started at centre-back in Liverpool's 4-1 win over Leicester at the start of September, in a match which saw the Reds taking chances with the way they were playing out from the back.

Again, there's nothing wrong with that when it works. Only thing was you'll remember Lucas providing a wonderful assist (from a Leicester perspective anyway) for Jamie Vardy.

Just like certain formations and positions can go in and out of fashion, don't expect the centre-back to disappear of course.

But if football, as expected, to a degree, is to move to the notion of universality (a sort of multi-purpose style that moves away from "specialists" in positions as explained here) at the highest level, then we could see more midfielders, ball-players or full-backs being thrown in to anchor back fours more often.