Wesley Fofana's physicality, defensive prowess and ball-carrying ability is making the difference for Chelsea

Graham Potter's switch to a back three has provided the platform for Chelsea's recent improvement but it is a question of personnel too. Wesley Fofana's return has made a difference.

The centre-back, a £75m signing from Leicester in August, has spent most of the season on the sidelines due to injury but Thiago Silva's withdrawal against Tottenham last month saw him thrust back into the side from the bench. He has started every game since.

Chelsea won the first three of those games, against Leeds, Borussia Dortmund and Fofana's former club Leicester, and they probably would have won the fourth, against Everton, had he not been forced off with what Potter termed "fatigue" in the closing stages.

Everton's equaliser in that 2-2 draw came from precisely the position Fofana had occupied two minutes earlier, with Trevoh Chalobah, his replacement, dragged too far wide, and Kalidou Koulibaly left exposed and unable to stop Ellis Simms amid the disarray.

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Koulibaly received heavy criticism for the ease with which he was beaten by Simms but it is worth noting that, according to Opta, it was the first and only time he was dribbled past all afternoon. His problem was that Fofana was no longer there to offer protection.

The 22-year-old subsequently had to be withdrawn from the France squad having received his first senior international call-up after that game, but the hope for Chelsea is that he will be fit to face Aston Villa on Saturday. Recent evidence suggests they will need him.

Over the course of the campaign, including the four appearances he made before suffering his knee injury in October, Chelsea have a record of six wins from eight games with Fofana starting, compared to only nine wins from 29 games without him.

His injury problems have been such that he remains something of an unknown quantity to many Chelsea fans - "you don't know how good this kid is yet," quipped the Leicester-supporting Gary Lineker recently - but his importance is not lost on Potter.

"We've missed Wesley," said the Chelsea manager after Fofana marked his first start in five months by scoring the only goal in the 1-0 victory over Leeds at Stamford Bridge earlier this month.

"He brings something different; physicality, he defends big spaces, he allows us to defend a little higher because he has the pace to recover. In the box, he can attack the ball well."

Brendan Rodgers, his manager at Leicester, called it "defending forward" in an interview with Sky Sports and Fofana typifies it.

"It is about anticipation, closing the pitch, sustaining attacks," said Rodgers. "You can be up there pressing but if [your centre-backs] are sat back on the halfway line then the pitch is too big."

Fofana enables his team to bring their defensive line forward by being aggressive when anticipating danger and timing his tackles and interceptions smartly, while, as mentioned by Potter, also being quick and alert enough to deal with passes in behind.

There is data to prove it. According to Opta's advanced metrics, Chelsea have played nearly three meters further up the pitch in the Premier League games Fofana has started under Potter, their average start distance - which measures how far upfield a team begin their passing sequences - leaping from 41.7m to 44.3m.

That higher start distance puts them roughly in line with Arsenal and Manchester City this season and, as with those two sides, it allows Chelsea to pin their opponents back and dominate them.

Chelsea find that more difficult when Fofana is not there and his ability to attack the ball is missed too. He has scored twice in only 10 appearances this season. As well as his towering header against Leeds earlier this month, there was a low finish in the Champions League game with AC Milan in October following another set-piece.

At the other end, Chelsea have only conceded three goals in his last 481 minutes on the pitch, and just as important as what he gives them inside the two boxes is what he offers in between them.

Fofana is a modern centre-back who, to quote Potter, is "brave on the ball", both in terms of his distribution - he is making more passes in the opposition half per 90 minutes than any other Chelsea centre-backs this season - and, crucially, through his ball-carrying.

Chelsea lost something in that regard with Antonio Rudiger's departure to Real Madrid last summer. The Germany defender's rampaging forward runs had become a feature of their play.

But Fofana has demonstrated the same capability, albeit on the opposite side, playing, as he does, on the right, rather than the left of Chelsea's back three, and the statistics prove it.

According to newly-available tracking data, the Frenchman in fact ranks fourth of all players in the Premier League this season for carries per 90 minutes, behind only Manchester City duo Jack Grealish and Bernardo Silva and Newcastle's Allan Saint-Maximin.

A deeper look at the data - which defines a carry as a touch event where a player travels 10 meters or more in possession of the ball - shows he ranks third for defenders bypassed per 90 minutes through carries (7.8) and sixth for distance carried per 90 (233m).

His carries give Chelsea an extra dimension when attempting to break down opposition defences.

Consider this 28th-minute example in the win over Leeds.

Fofana receives Enzo Fernandez's square pass in the centre circle and immediately drives into the space in front of him.

His run draws both Jack Harrison and Tyler Adams towards him, simultaneously freeing up Ruben Loftus-Cheek and Raheem Sterling.

Sterling is then able to receive Fofana's pass in a pocket of space between the lines as Loftus-Cheek makes an untracked run on the outside, giving Chelsea the chance to breach the Leeds defence.

There was a similar example in the second half of the same game, as shown below.

Fofana again picks up possession just inside his own half, and again opts to carry the ball forward rather than seek an early pass.

By doing so, he again draws Adams out of position before timing his pass so his team-mate, this time Fernandez, is able to turn into space in the final third, creating another dangerous situation.

Fofana usually drops back into position once he has released the ball following a carry but on some occasions he continues his run, his presence high up the pitch giving Chelsea an extra body in attack and enabling them to catch their opponents by surprise.

There was an example against Crystal Palace earlier in the season.

Fofana is once again immediately on the front foot having received Thiago Silva's pass, accelerating into the space in front of him and taking two Palace players out of the game as he drives between Odsonne Edouard and Wilfried Zaha.

From there, he lays the ball off to Sterling to his right and continues to charge forward, untracked, giving Chelsea an overload on the left-hand side of the Crystal Palace box.

This combination with Sterling could be seen in the win over Leeds, too, with Fofana again carrying the ball forward, as shown below, then playing a square pass to his team-mate before running into a gap between two defenders to give the option of a pass in behind.

So, at the same time as allowing Chelsea to change the way they defend, Fofana gives Potter an additional weapon in attack.

It is just another reason why, despite his limited involvement, the Frenchman is uniquely important to the Chelsea manager.

It remains to be seen whether he will be available for the visit of Aston Villa on Saturday. But what is certain is that Chelsea are a different proposition with Fofana in the team.

Watch Chelsea vs Aston Villa live on Sky Sports Premier League and Sky Sports Main Event from 4.30pm on Saturday; kick-off 5.30pm

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