Sunderland boss Dick Advocaat wants more reinforcements to strengthen a defence which has conceded 11 goals in four games so far this season.

"I'm happy with the six goals, but totally unhappy with the way we gave three goals away. That has to improve and the players know that," said Advocaat, who has already signed three defenders this summer.

"I am wondering if it is to do with concentration, sharpness - it cost us three goals, and that's a worry. And it's not the first time."

Manchester City's Belgium international defender Jason Denayer has been mentioned as a possible target for the Wearsiders, but Advocaat played down the move.

"There has been talk about the young guy from Manchester City, but he is going to another club," said Advocaat.

"We are still looking, but when (Younes) Kaboul is fit, he's a very good player."