After last season's stability at the back, Chelsea have struggled to keep the ball out of their net this season.
They have just five clean sheets in their last 14 games in all competitions, which seems quite poor when you realise that Manchester United have kept eight in the Premier League alone in 11 matches.
Antonio Conte has rotated regularly with his defensive players and formations, switching between four and five at the back.
Chelsea brought Antonio Rudiger and Davide Zappacosta to the club in the summer and welcomed Andreas Christensen back from a loan spell, while retaining their assets that took them to the Premier League title last term.
David Luiz didn't even make the squad for yesterday's 1-0 win against United at Stamford Bridge, in what Conte labelled a 'tactical decision'.
However, it has been revealed that the Blues missed out on another defensive target on deadline day, which was also when Zappacosta joined.
PSG full-back Thomas Meunier has claimed he turned down the chance to sign for Chelsea on the final day of the transfer window, instead deciding to stay and fight for his place at the Parc des Princes.
The Parisiens added Dani Alves to their ranks over the summer, something which the Belgian thought would force him out of the door.
He's started six of their 12 games in Ligue 1 in his second season in the French capital, having signed from Club Brugge in 2016.
Despite the fierce competition from one of the best-right backs in Europe, Meunier says he is happy in Paris, and wants to establish himself as a regular in the side.
"I was expecting PSG to sign another right-back, but didn't foresee them getting Dani Alves," he told Belgian TV, per Sky Sports.
"I didn't know what to think. Was I going to remain on the subs' bench all the time?
"I could have left for Chelsea on the final day of the transfer window. But I didn't want to join them. I am happy at PSG and I don't want to leave."
Chelsea had also been linked with Alex Oxlade-Chamberlain before they turned to Zappacosta, though it appears he was their third choice behind Meunier.
The Belgian has started the season well at domestic and international level, scoring a hat-trick for the Red Devils against Gibraltar, and has three goals for PSG too, who lead Ligue 1 by four points.