Following Celtic’s defeat to Bayer Leverkusen on Thursday, Noel Whelan believes the club will want to acquire a new centre-back in January.

After surrendering three goals in Germany, Ange Postecoglou will aim to bolster up his defence, according to the former Aberdeen striker.

Postecoglou said to the Scottish Sun after the 3-2 loss that his players “are not at this level yet.”

The Hoops have surrendered 13 goals in five Europa League games, the most of any team in the group stages.

Whelan confessed that the Hoops’ defence had been a problem for the past year and a half.

“I think what he said about not being at that level, if they can’t fix the problem on the training ground, you’ve got to look elsewhere.

“That’s what you’ve got to do. There’s been a lot of slack defending from Celtic over the last season-and-a-half now.

“You can’t keep defending like that and conceding goals like that. There’s nothing better than seeing your team taking pride in keeping clean sheets.

“Right now, they’re struggling to do that. I think that’s the only one area, he’s strengthened in midfield, he’s strengthened in the forward line.

“He brought in two centre-halves in the summer but I do believe he needs to go into the market and probably get another centre-half.

“There’s probably no doubt in his mind he’d like to get another centre-half in. I can see that happening.”

Celtic added Carl Starfelt and Cameron Carter-Vickers, the latter on loan, to their center-back ranks.

Postecoglou’s other senior choices at the heart of defence are Stephen Welsh and Christopher Jullien.