Chelsea have been very unstable at the back this season so far, and Cesar Azpilicueta is arguably the main reason.
The Blues have started the Premier League season in an unsatisfactory way, collecting one point from their first two games.
And one factor that has hampered them so far this season has been their defence.
Chelsea are usually known for their defensive solidarity, but under Frank Lampard, it has looked a completely different story so far.
The West-Londoners have already conceded five goals in two Premier League games, including their embarrassing 4-0 defeat to Manchester United on opening weekend.
It has gone all defensively downhill since last season
Chelsea were not great defensively last season, but they weren't this bad in the defensive aspect.
One major difference from last season has been the personel in the back four. Last season David Luiz nearly played every Premier League game under Maurizio Sarri.
The Brazilian was not great defensively but offered proper leadership to the back four. And him now leaving to Arsenal has filled a void of a lack of leadership in that back four.
This season there hasn't been a proper leader in that back four to organise the unit when it has been disorganised.
The other major personnel change has been not having Antonio Rudiger in that back four. Unfortunately, he has been out injured, but he seems to be on the road to recovery, so once he's back- we may see a bit more defensive stability in that back four.
The players in the back four who aren't the problem
There are two players in the back four who haven't been the main culprits for Chelsea's defensive woes.
The first player who definitely isn't the problem, and who has arguably improved one position in that back four is Emerson Palmieri.
The Italian full-back has started this season really well and has been a major upgrade on last seasons main left-back Marcos Alonso.
The Chelsea left-back is more defensively reliable than Alonso, and every week is showing major signs of improvements to his game.
The second player who arguably isn't the problem in the back four is Andreas Christensen. Now in my opinion and many other Chelsea fans opinions- there are major signs of improvement in his defensive game.
And still, at such a young age- he could be a Chelsea centre-back for the long-term future.
The Danish centre-back hasn't been the main fault for any goals that have been conceded this season.
The players in the back four who are arguably the main problem
The first player who is a problem in the back four, but isn't the major one is Kurt Zouma.
The Frenchman started the season in awful fashion against Manchester United. He conceded the penalty which helped United go 1-0 up whilst Chelsea were on top at that time. And for the whole game seemed a massive liability.
However, Zouma's performances have improved slightly since the opening weekend. He and Christensen were very solid against Liverpool in the Super Cup, and for the first half of the Leicester City, game were solid.
With Zouma he just needs time to settle into playing first-team football regularly for a team like Chelsea. Once he's settled, we will see the best Zouma and what he really can offer to Chelsea.
The main problem in the back four is arguably Cesar Azpilicueta. Last season he looked suspect at right-back under Sarri, but this season so far has shown how far he has declined.
As a right-back, he can't cross a ball, he gets beaten by pace and that put together with the fact that he struggles to see runs in behind him means that he is a massive liability.
Chelsea have conceded seven goals in all competitions so far this season, and the main culprit for 80% of those goals has been Azpilicueta.
The first solution in solving Chelsea's back four woes is to bring back Antonio Rudiger into the back four once he is back fully fit again.
That should be very soon, as Rudiger played in Chelsea's U23s 3-0 win over Liverpool in Premier League 2.
And the main solution is to get Reece James into the team as soon as possible to replace Azpilicueta.
Adding Reece James to the team adds pace and freshness to that right-back position which needs altering.
And it looks like Frank will show trust in the Chelsea youngster after Davide Zappacosta looks like he will be leaving on loan to AS Roma later this week.
Furthermore showing his trust and faith he puts in the young English right-back- who received player of the season for Wigan Athletic last season.