Laurent Koscielny Holds the Key for Arsenal vs. Southampton

Laurent Koscielny returned to Arsenal's ranks for their win at West Brom on Saturday, and his presence will be crucial for the Gunners once more when they host Southampton on Wednesday.

Returning after almost two months out with what David Hytner of the Guardian called "Achilles trouble," the Frenchman was stationed at centre-back at the Hawthorns.  Immediately, Arsene Wenger's side reaped the benefits of Koscielny's presence.

The result: scoring the Gunners' first win and clean sheet in three Premier League showings.

With the France international back in the fray, the entire back four is boosted and buoyant—even if the Gunners are now without a fully fit left-back. 

With both Kieran Gibbs and Nacho Monreal doubtful for the Saints' visit, per Arsenal.com, Koscielny or Calum Chambers are set to deputise on the flank, so says James Olley of the Evening Standard.

Now, with a shaky Southampton travelling to the big smoke, Koscielny's habitation in the back four is set to hold the key for an Arsenal triumph in this midweek clash.  Where he fits into Wenger's plans can have a massive impact on the game.

Koscielny's Irrefutable Impact

It's easy to wax lyrical about how Koscielny impacts Arsenal's defence when he's fully fit.

Now in his fifth season at the club, he has matured into a world-class defender, such is the view of team-mate Santi Cazorla.  The Spaniard grouped Koscielny with Alexis Sanchez and Mesut Ozil as Arsenal's three best players, per Tom Sheen of The Independent:

"Looking elsewhere, Laurent Koscielny for me is a great defender and there are very few players like him in the world.  Of course I could give you more but I think these three are good examples."

Crucial to this perception of Koscielny is one of his finest traits—his pace—which in turn complements his positional nous and determination.

This is particularly vital for Arsenal given their defensive personnel.

The resolute yet stationary Mertesacker will fill one of the central roles at the back, and it's that pace of Koscielny which makes the German effective.

Mertesacker is notoriously slow—slower than Internet Explorer, according to a participant of an Arsenal question-and-answer session on Twitter, per The Independent.  Koscielny's swiftness of foot and his agility allow him to deter speedy strikers and make quick changes of position, freeing up Mertesacker to distribute play from the back.

This mechanic was evident in the West Brom clash and it improved the entire defence, as Squawka's Thomas Hallett noted:

The whole defence looked comfortable, settled. There were two full-backs who were accustomed to their roles, and the first-choice (and admittedly only) centre-back partnership.

Monreal proved to have very few of the qualities Koscielny has that made him and Mertesacker stand out as they did last season. The full-back isn't strong enough, tall enough, good in the air, or capable of making the kind of last-ditch tackles that has seen Koscielny bail out the team and Mertesacker in the past.

So with the Frenchman finally back in action, how he is used going forward will be crucial for Arsenal's chances.

Keep Koscielny Central?

In this potential system for the Southampton clash, Wenger would keep Mertesacker and Koscielny together in the middle, forcing Chambers out to the left and introducing Hector Bellerin at right-back.

With Koscielny patrolling the centre of defence, Arsenal will have someone more than capable of dealing with the scheming Dusan Tadic. 

The Serbian is set to play a pivotal role considering the absence of Morgan Schneiderlin.  As such, Koscielny's presence will be vital to dealing with the likes of him and Sadio Mane, Southampton's creators-in-chief.

Furthermore, this allows a favourable matchup on set pieces with Mertesacker free to counter the physicality of Graziano Pelle.  The Italian might be without a goal in his last four appearances, per WhoScored.com—but having netted six times so far this campaign, he has proven himself a perennial threat.

Of course, the inevitable drawback here is that Chambers is unaccustomed to the left side of defence. 

The 19-year old has belied his years with some performances of genuine maturity, but his inexperience hasn't gone unnoticed (see Jefferson Montero's performance for Swansea).

Fielding him on the left is certainly a risk, but Wenger is left with few alternatives.  If nothing else, Le Professeur is nigh on guaranteed a lively, heartening showing from Chambers.

Push Koscielny Out Wide?

Another possibility for Wenger, although not one to recommend, would be to jettison the Koscielny-Mertesacker combo in favour of utilising the Frenchman on the left.  This would bring Chambers inside.

The reason why this notion deserves consideration is that Wenger loves to deploy his full-backs as marauders.

He's prone to sending his full-backs on missions up and down the flank, providing offensive support—often at the expense of proper defensive cover.  Although with the injury problems that have beset Arsenal, it might make plain sense to some to abandon those plans in favour of a more conservative approach, Wenger has had other plans in the past.

The games against Swansea and Anderlecht, to name but two, have seen such tactical patterns take hold with dire consequences, yet Wenger has shown himself willing to carry on with the plan.

With this in mind, he may favour Koscielny as a more "complete" player than Chambers for this role.  Able to get forward and back without hassle, Koscielny would be more reliable than the young Englishman, certainly in a defensive sense.  However, given the various strengths and vital experience Koscielny brings to the centre of the park, Wenger must keep Koscielny central.

This is only embellished when considering the drought of experience in Arsenal's goal.  Emiliano Martinez has coped fine thus far deputising for the injured Wojciech Szczesny, yet he can only benefit from Koscielny sitting in front of him.

Wherever Koscielny plays on Wednesday, it's utterly evident that him playing will be a huge boost for Arsenal, as it was against West Brom.

It's not long until January, and Mathieu Debuchy might also return to boost the numbers sooner than expected, via The Telegraph's Jeremy Wilson.  Reinforcements could prove to be en route, en masse.

For now, though, Koscielny holds the key to Arsenal's success, playing forward from the back.  He's the single most important defender in Arsenal's squad—as his performances will prove.

What do you make of Koscielny's return to action? Get the debate started with a comment, or make a point on Twitter.