One of Liverpool’s biggest problems post-World Cup persisted against Newcastle United on Saturday, despite the return of Virgil van Dijk. Jürgen Klopp must fix it.

This week, Liverpool manager Jürgen Klopp has been boosted by the return of numerous first-team players who had been sat on the sidelines with injuries.

In attack, Diogo Jota and Roberto Firmino are both back in the fold, having been missing since October and December respectively. And at the other end of the field, Virgil van Dijk has recovered from the hamstring injury he suffered in the 3-1 defeat against Brentford six weeks ago.

Van Dijk was an unused substitute in the 2-0 Merseyside derby win over Everton on Monday and then slotted back into the starting line-up against Newcastle.

While he’s been some way from his absolute best this season, the hope was that his return would help shore up Liverpool defensively.

The Reds have looked vulnerable in open play throughout the campaign, mostly because of their well-documented frailties in midfield, but recent set-piece struggles have made matters even worse.

Prior to the World Cup, Liverpool was conceding 2.2 set-piece shots per game but in the 12 matches since (barring Wolves away because the data is unavailable), it has been allowing 3.2.

One extra attempt may not sound all that bad, but the results have been alarming. Before the tournament in Qatar, Liverpool had conceded two set-piece goals in 15 matches against Premier League opposition.

But in the 12 games since the resumption of the club season, it has given up six — three in the league and three in domestic cups.

Van Dijk’s return was supposed to restore Liverpool’s strength in defensive dead-ball situations.

Yes, Liverpool had struggled badly against Brentford even in the 45 minutes the Dutchman played, and its set-piece record had been on a steady downward trend since the 1-0 defeat at Forest back in October anyway (as explored here).

But you could see why many drew a link between the center-back’s absence and Liverpool’s woes. As a commanding aerial presence, a calming influence and, most of all, the chief defensive orchestrator, he should at the very least have alleviated the situation.

Indeed, Liverpool had conceded three set-piece goals in 16 with Van Dijk, and five in 12 without. But against Newcastle, there was no improvement. In fact, things got considerably worse.

The Magpies recorded a whopping seven shots from set plays, more than any other opposition team this season. The combined xG (a figure that rates the likelihood of a goal from 0.01 to 0.99) of these chances was only 0.68, but at least two of them very nearly resulted in goals.

First, Dan Burn — yes, the 1.98m Dan Burn — was afforded way too much space on the edge of the six-yard box, and crashed a header off the crossbar after meeting Kieran Trippier’s delivery.

Then, 10 minutes into the second half, Newcastle loaded up the far post with four bodies, and Fabian Schär headed a ball across goal that, ironically, was begging to be tapped in at the near post.

Liverpool matched Eddie Howe’s side numerically at the back stick but still, Schär was able to shake off Trent Alexander-Arnold for a free header. Had either of these chances gone in, the outcome could easily have been very different in a crucial game for Liverpool, even against 10 men.

If Van Dijk isn’t going to be answer, then it’s down to Klopp and his coaching staff to address this urgent issue on the training ground.

And they would be wise to change things immediately, because their next opponents — Real Madrid — have scored eight set-piece goals in La Liga this season, the joint-best record in the league.