Liverpool are not top of the Premier League. They are second behind Manchester City on goal difference. After a weekend away with the FA Cup, then diverting matches in Europe, it is probably worth remembering that sobering fact.

True, Liverpool have a game in hand. And, with City occupied in the League Cup final against Chelsea, Sunday’s trip to Manchester United is effectively that game.

There is always an assumption that games in hand are won, but if ever a Liverpool game was not in hand, it is at Old Trafford. The Merseyside Reds have had two victories in their last 10 league visits to a stadium they never refer to as the Theatre of Dreams.

Should Liverpool lose at United they will have played the same number of games as City and will have the same number of points – 65. But City’s goal difference will be superior by at least 11, which, when the season is done, acts as a point.

This might sound like a downbeat analysis, but it is realistic. As it stands, Liverpool are second.

This, however, is the chance to jump back into the lead and, for Jurgen Klopp and his players, victory at their greatest rivals would also bring momentum for next week. There is Watford at home on Wednesday, then Everton at Goodison Park next Sunday. Eight days a week.

Packing United-Liverpool into a three-game sequence is questionable. This is a stand alone fixture and has been since Liverpool surged under Bob Paisley in the 1970s and eclipsed their red rivals.

Even before then, the civic animosity saw Nobby Stiles hit by a dart at Anfield in the 60s.

There have been other moments of friendship between the clubs but the fanbases have entrenched and for all that Alex Ferguson revered Bill Shankly and Paisley – and Klopp no doubt admires Ferguson – no player has been transferred directly between the clubs since Phil Chisnall left United for Anfield in 1964.

In 2002 Ferguson responded to a comment from Alan Hansen that United were facing a tough challenge by saying his greatest had been “knocking Liverpool right off their f------ perch.” Ferguson was not smiling when he said this.

Ole Gunnar Solskjaer mentioned his former manager on Friday, saying Ferguson could come in and give the team-talk just to let the United players know what a Liverpool win would mean.

The Herald:

READ MORE: Scottish Premiership referees' stats revealed

Remember, Jose Mourinho lost his job at United after the meek 3-1 loss at Anfield in December. These are encounters with consequences.

It is all part of the pre-match propaganda. Beyond parochialism the result has meaning for United because they are in a race with Arsenal and Chelsea for next season’s fourth Champions League place. If Solskjaer was buffeted by the home defeat by Paris St. Germain in the Champions League, he and his squad recovered impressively to deliver a composed 2-0 win at Chelsea in the FA Cup on Monday night.

United have been recognisably United since Solskjaer took over. Marcus Rashford, who scored the two goals that beat Liverpool on their last visit, has six in the 12 Solskjaer games – as opposed to four in the previous 4-and-a-half months.

For Liverpool, United’s rediscovered ambition is both threat and opportunity. Klopp’s defence have just registered successive clean sheets – at home to Bournemouth and Bayern Munich – which is welcome after conceding against Crystal Palace, Leicester and West Ham in a period when external doubt rose.

But to win – and it is a win which would be a declaration of title intent – Liverpool must score. Klopp will certainly be reminding his players that in United’s last home League game, Burnley were 2-0 up, and for all the praise heading Victor Lindelof’s way recently, there is still a collective vulnerability about United’s back four. That David De Gea remains the side’s most important player says something.

It is one of those intriguing facts that Mo Salah has scored against all current Premier League clubs except United. It would be some day to alter that. Salah has been prepared to acknowledge “the pressure” at the top.

When Liverpool last won at Old Trafford – under Brendan Rodgers in March 2014 – it was not quite the same. Steven Gerrard and Co began the day seven points behind leaders Chelsea and the pre-game talk was about eliminating David Moyes’ United from the top four. “The first job is to consolidate fourth,” Rodgers said.

Liverpool’s 3-0 win – two from Gerrard, one from Luis Suarez – changed that. Suddenly Rodgers’ team were serious contenders. And they had a game in hand on Chelsea, which they won.

The momentum gained carried Liverpool a long way, if not to the end. Klopp, and the Kop, will be hoping for a repeat performance. Then the title game will be in Liverpool’s hands.