Dejan Lovren
Dejan Lovren joins the Reds from Southampton but has failed to make the step up requiredGetty Images

Liverpool must address their expensively assembled defence during the January transfer window in order to rescue their top-four hopes, according to former Reds player John Scales.

The Merseyside giants' campaign has been undermined by errors at the back that is threatening to see them miss out on the Champions League next season.

While Simon Mignolet's performances have come under fire, Mamadou Sakho and Dejan Lovren have come in for criticism for a series of uncertain displays for a Liverpool side who are five points adrift of the top four.

The club have also suffered problems in the attacking third, with Rickie Lambert, Fabio Borini and Mario Balotelli having scored just one league goal between them this term, and Scales says it is inevitable Liverpool will enter the market at some stage.

"It's difficult for Liverpool," the former defender told Sky Sports News. "You look at past January transfer windows and the transfer policy generally and there have been one or two hits and one or two misses.

"In the last year, Adam Lallana has started to come good, [Lazar] Markovic has shown the talent and skill that he has got, [Philippe] Coutinho has come in and done very well and Sterling has had a fantastic couple of years.

"Then you have players who are still trying to settle in; Lovren, Sakho, they have been a bit disappointing, defensively they have been a bit all over the place. It's difficult to rebuild the team in January to go in the market and spend a lot of money.

"If Balotelli goes, do they bring [Divock] Origi back from Lille or do they go into the market and get Berahino? We are going to be in for an interesting second half of January but they will certainly dip into the transfer market if they can."