Jurgen Klopp's Liverpool struggled to break down Manchester United

“They were purely there today to defend us,” Jurgen Klopp told Sky Sports after seeing his Liverpool side frustrated against Manchester United. The Premier League leaders needed a late goal from Adam Lallana to escape Old Trafford with a point but Klopp did not get out of the building without a pithy line from Jose Mourinho fired off in his direction.

"He didn't like the menu," Mourinho told Sky Sports.

"He likes meat and he got fish."

1:38 Jose Mourinho claimed Liverpool struggled to cope with United's tactics Jose Mourinho claimed Liverpool struggled to cope with United's tactics

Asked what Liverpool were lacking on the day, Mourinho added: "For me, it was quality as a team to play against a low block which is a problem that they sometimes have. I think they have some limitations against teams that play with a low block."

Liverpool struggled for fluency all afternoon, scoring from the one clear-cut opening that they created when Andrew Robertson's low cross somehow found its way to the substitute Lallana at the far post.

Liverpool were restricted to only a few opportunities against Manchester United

Mohamed Salah was missing through injury but even with the star man absent it was still unusual to see Liverpool restricted like this. The club's own supporters would surely concede there is some truth to Mourinho's comments. Klopp's side seem to find it harder to be at their devastating best when they are denied space in behind in which to run.

Indeed, one of the great strengths of Klopp's team in 2019 has been the ability to find a way to pick up wins even when opponents try to neutralise their greatest strengths. They have been patient. Won in different ways. Nine games in and Liverpool are still six points clear of champions Manchester City. The problem is clearly not insurmountable for them.

2:56 FREE TO WATCH: Highlights from Manchester United's draw against Liverpool FREE TO WATCH: Highlights from Manchester United's draw against Liverpool

But it is a challenge and Manchester United's decision to switch to a back five for the first time this season proved a tricky one for Klopp's team because it denied them even more space. Not only was there no room for the forwards to run into, the formation also caused difficulties for that other great weapon of this Liverpool side - the marauding full-backs.

"The problem all teams have against Liverpool is that they play a back four and the back four goes really narrow because they have to with the front three making those runs all the time," Gary Neville told Sky Sports.

"So the full-backs get in all the time."

Although Robertson did provide the assist for Liverpool's goal, there is no masking the fact that the full-backs were not as effective as usual.

It is becoming an issue for Trent Alexander-Arnold this season when playing against a five-man defence because the opposition wing-back is able to stay that little bit wider. It means that the youngster - such a threat when able to get further forwards - frequently finds his path blocked.

1:14 Graeme Souness claimed that some of Liverpool's players just didn't turn up Graeme Souness claimed that some of Liverpool's players just didn't turn up

"Liverpool are at their most threatening when they get it wide," added Graeme Souness. "Especially Trent Alexander-Arnold with the way he whips the ball in. But he was crossing from the wrong angles. He couldn't get down there and put the ball behind the last man."

All eight of Alexander-Arnold's open-play crosses failed to find a Liverpool team-mate. "He could have done more and done better with them," Klopp told Sky Sports. That's true. But the big problem was where the crosses were coming from. Alexander-Arnold's touch map from open play shows that he rarely managed to get within 20 yards of the goal line.

Trent Alexander-Arnold's open play touch map for Liverpool at Manchester United

In his previous game against Sheffield United, he also found himself up against a back five and that had a similar effect on his impact. He didn't create a single chance from open play in that game and didn't have a touch inside the opposition penalty box either.

Having also played against a back five against Southampton and Newcastle this season, the contrast in his creativity can be seen in the stats. According to Opta, in the five Premier League matches against a back four this season, Alexander-Arnold has created six big chances. In the four games against a back five, he has created only one.

With Alexander-Arnold unable to play his natural game and the forwards unable to run in behind, Liverpool looked a different team on Sunday. Neville added: "Manchester United did everything to stop those two main threats and they left the ball with Fabinho in midfield or Jordan Henderson in midfield and they have not got the quality to be able to unlock."

Jordan Henderson's passing sonar for Liverpool against Manchester United

Henderson's passing was too safe and with Fabinho struggling to pick a way through too, it was often left to Joel Matip to attempt to thread the passes through to Roberto Firmino.

The centre-back actually found the striker more times than Henderson and Gini Wijnaldum combined but that is not likely to be a reliable basis from which to build play in the long term. It is interesting that late substitute Naby Keita's more incisive passing played its part in the build-up to the equaliser. He was looking for the angles that others were not.

"Naby in the end maybe came on too late but the influence was there," said Klopp. "We had the passes. We had them where we wanted to have them."

Liverpool salvaged a point in the end and - as Henderson told Sky Sports - that could yet prove to be important in the Premier League title race.

But while Klopp was left frustrated by the manner of Manchester United's performance, he might have to expect even more of this sort of thing after this. The Liverpool manager is already accustomed to teams defending deep against the European champions. But it is now becoming clearer that there is a particular formation best suited to stifling his team too.