How will Chelsea line up with David Luiz back at Stamford Bridge?

On a typically frenetic conclusion to the summer transfer window, David Luiz's sensational return to Stamford Bridge proved to be the day's biggest head-scratcher. Two years ago, Chelsea were heralded as kings of the mercato for squeezing £50m (€59.3m) out of Paris Saint-Germain for the defender.

Now he is back, and by his own admission, has unfinished business in the Premier League.

Given the timing of the deal, it is clear the Brazil international was not Antonio Conte's first choice. Napoli's Kalidou Koulibaly, Juventus stalwart Leonardo Bonucci and another Brazilian plying his trade in Paris, Marquinhos, were all reportedly ahead of Luiz in the queue.

Chelsea have begun the season with just two fit centre halves in 35-year-old John Terry and Gary Cahill. Kurt Zouma is not expected to be fit until the end of September. Chelsea's need for another option was one of their biggest dilemmas of the summer; not bringing in another body simply wasn't an option.

Opinion on Luiz varies. 'The geezer' is an undisputed cult hero among the Chelsea contingent and was exceptional on the club's most famous night; the Champions League triumph over Bayern Munich in 2012. But individual errors and lapses in concentration never really faded from his game during his first spell at Stamford Bridge. They didn't at PSG either, with his disastrous last appearance for the Ligue 1 champions acting as a firm reality check for anyone thinking Luiz will return to the Premier League a changed man.

A manager as defensively-savvy as Conte would surely not have signed off on a transfer without having an idea of how to bring the best out of the crowd favourite, however. IBTimes UK considers how Chelsea will line up with one of their favourite sons back in the mix.

Antonio Conte's 3-5-2 formation

Conte's success with Juventus and with Italy at Euro 2016 was built on his 3-5-2 formation and, more specifically, the immovable presence of Gianluigi Buffon in goal and the centre-half trio of Andrea Barzagli, Leonardo Bonucci and Giorgio Chielleni. A simple lack of options in that position have prevented the Italian from using that formation in the Premier League, but the arrival of Luiz could pave the way for its introduction.

In order for the 3-5-2 to work effectively, one of those centre-halves has to be comfortable on the ball, adept in bringing it out from the back and sparking moves further forward. Bonucci performs that role expertly for club and country. Luiz lacks the defensive solidarity of the 29-year-old, but possesses the similar ability to drive forward and provide a telling pass. Alongside the sturdier presences of Cahill and Terry and with N'Golo Kante tirelessly cleaning up if he gets caught too far forward, Luiz could find himself operating there.

Sticking with a 4-3-3

The above would call for Conte to change a system that has guided Chelsea to three wins from three in their opening games of the new Premier League season. Should he stick with four at the back, with Cesar Azpilicueta and Marcos Alonso slotting in at right-back and left-back respectively, Luiz would partner either Terry or Cahill. It's a system the 30-year-old has operated in for much of his career, but as we all know, occasionally at a cost to his side. Terry's leadership and the presence of Kante in front of him would, at a glance, reduce that risk, however. But is it a risk Conte will take on a regular basis?

4-2-3-1 with David Luiz in midfield

When Luiz was at his most unreliable, he occasionally moved forward to take up a midfield role. Firstly under interim manager Rafa Benitez and then under Jose Mourinho during his return to Stamford Bridge, the Brazilian impressed further forward where his defensive shortcomings weren't quite so brutally exposed.

In February 2015, Luiz lined up in the same position as a PSG player with Thiago Motta and Yohan Cabaye ruled out injured in a Champions League clash against his former club. In that game, his defensive nous was again lacking, allowing Branislav Ivanovic to run off him to score Chelsea's opener. But he excelled further up the pitch, finding teammates with pinpoint passing and coping in physical battles with Cesc Fabregas and Diego Costa.

It could be an option at Stamford Bridge once again with the presence of Kante and Luiz making a rather conservative but water-tight unit to sit in deeper midfield roles.

It hardly solves Chelsea's problems though. They needed a centre-half. They only have three, one who will be returning after a serious knee injury in four weeks' time. Signing one who instils so little faith when playing in his natural position that he has to be moved elsewhere would be nothing short of ridiculous.