Kalidou Koulibaly had impressed in the game against Tottenham, where he scored a brilliant goal from a corner kick.
The 31-year-old Senegal international was signed up to replace the departed Antonio Rudiger in the left centre-back role.
Koulibaly was defensively poor against Southampton, and his performance against Leeds United was also very shocking, as he saw red in that game.
Former Chelsea defender Frank Leboeuf has slammed Koulibaly’s performances for Chelsea and has said the defender isn’t there yet.
“They miss so much [N’Golo] Kante in the middle of the park you know to get the ball back, to put some level of pace that they don’t have with Jorginho,” Lebouef told ESPN.
“With Kovacic they get a little bit more but defensively in middle of the park nobody near it. You win your battles and you win your games in the middle of the park.
“On top of that Koulibaly is not there yet. He had a good goal against Spurs but defensively he’s not there yet.
“On the second goal they conceded with Thiago Silva they don’t talk to each other. They both follow Adams but Armstrong is free, so there’s many things to adjust in order to get something.
“Worryingly, they’re already there. Four games, 8th in table, if others like Arsenal win they can be too far away already. It’s not enough, really not enough.”