Jamie Carragher has called on Liverpool to sign a left-back in the January transfer window, claiming it will boost the club’s chances of winning the Premier League title.

Those hopes took a slight hit on Sunday when Liverpool was held at home by Manchester United, meaning the Reds’ lead at the top of the table has been cut to six points with a game in hand.

While Cody Gakpo and Mohamed Salah’s goals ensured Liverpool’s threat up front continued, the Reds looked less certain at the back. Lisandro Martinez and Amad scored for Ruben Amorim’s side, who managed 13 shots at Anfield.

READ MORE: Liverpool January transfer plans laid out as Reds linked with free agents

READ MORE: Virgil van Dijk finally broke and screamed at Trent Alexander-Arnold before he was hooked for Liverpool

• Virgil van Dijk fumes at Liverpool teammate as Arne Slot proven right - 5 talking points vs Man Utd

• Jamie Carragher confirms Liverpool's worst Trent Alexander-Arnold fear after Man Utd draw

Trent Alexander-Arnold took most of the criticism, but Andy Robertson didn’t impress either. Particularly for Amad’s late equalizer, the Scotland international didn’t react quickly to Alejandro Garnacho’s cross into the box.

It’s not the first time this season Robertson’s contribution has come under scrutiny, and Carragher said Liverpool needs to strengthen in that position urgently.

"Liverpool need to sign a full-back. I think they need a left-back,” the 46-year-old said during Sky Sports' post-match coverage. "Trent Alexander-Arnold was really poor. He will be a lot better than that and Conor Bradley is fantastic. I just think Andy Robertson, who is an absolute legend, is just hanging on in every game.

“I don’t think Kontas Tsimikas is quite of the standard to come in and replace him. I think if Liverpool could get a left-back in January, I think that’d put Liverpool in a really strong position to win the league.”

It’s not the first time Carragher has offered this opinion. “He [Robertson] needs help, doesn’t he? Tsimikas, he’s not at that level, we know that,” the former defender said last month. “But Robertson is playing too much football. He can still do 15-20 games a season, but he needs help in January.”

As for Robertson, he’s aware of the criticism. “Last couple of games I've been on the bench and I got doubters for the first time in a long time, first time at this club," the ex-Hull City man said in November. "But it suits me in this position. I am trying to prove people wrong again.”

It’s likely he will be given a rest for the upcoming games against Tottenham Hotspur and Accrington Stanley in the cup competitions, before Liverpool returns to Premier League action in nine days’ time with a top-of-the-table encounter against Nottingham Forest.