Martin Skrtel
Skrtel was given the run--around by Ighalo throughout Watford's 3-0 winGetty Images

Liverpool manager Jurgen Klopp must make significant changes to his defence during the January transfer window, according to former player Jamie Carragher. The Reds suffered their most harrowing loss since the German took over in October at the hands of newly-promoted Watford and the defeat reinforced the view the club needs fresh impetus.

Klopp had enjoyed a successful start to life on Merseyside but four games without a win has hit the club's Champions League qualification hopes and lowered expectations. At Vicarage Road, Quique Sanchez Flores' side outran and outmuscled their more illustrious opponents and strolled to a comfortable 3-0 giant-killing.

Former Liverpool defender Carragher believes Klopp's side have a weak spot after seeing Odion Ighalo net twice, the first coming after he overwhelmed the usually dependable Martin Skrtel, while they are also lacking in the goalkeeping department. Adam Bogdan made his Premier League debut for his new club instead of the injured Simon Mignolet but a third minute error which allowed Nathan Ake to score defined his performance.

Speaking on Sky Sports, Carragher said, according to Inside Futbol: "The performance and the result at Watford will be in his [Klopp's] mind for the rest of the season and it reminds me of [Gerard] Houllier and [Rafael] Benitez in their first season. The teams they inherited weren't able to cope physically with the Premier League –and this Liverpool team isn't.

"And what they did was both bought a keeper; both bought a holding midfield player. Benitez bought [Peter] Crouch, six foot 7 at the front and Houllier bought two centre-backs. Now if I was Klopp I'd be thinking goalkeeper, two centre-backs and a holding midfield player because Liverpool haven't got the players to cope in those physical games."

With Daniel Sturridge restricted to one start since Klopp's arrival, Liverpool have been lacking a focal point with Divock Origi and Christian Benteke flattering to deceive while Roberto Firmino's involvement in attack has been fleeting. Ex-forward John Aldridge says the whole of Liverpool's spine needs reinforcing, including the forward line.

"There is no doubt that the Liverpool squad needs strengthening in January," he told the Liverpool Echo. "We need more battlers because we're getting out-fought. It happened against West Brom and it happened again against Watford,

"As the old saying goes, you need to win the individual battles and then the quality shines through. We failed to win those battles at Vicarage Road. In terms of positions where we need to buy, you could go right through the spine of the team - centre-half, centre-midfield, striker."