If you're talking about the goal conceded against WHU, it's down to Skrtel's error. I've said it in a different thread and I've watched that goal a few times. Maiaga wasn't even attacking the ball. Had Skrtel attempted to head the ball instead of trying to reach it with his boot, there won't be a goal. If Maiaga had attacked the ball more fiercely, Skrtel would have connected his boot to Maiaga's head and that would be a stonewall penalty. It came down to Skrtel's dangerous play.
So far, Sakho has done very little wrong in the games he's played. Colossal player.