Liverpool picked up a vital win over Bournemouth on Saturday afternoon, but in the 75th minute of the bout, Jürgen Klopp was presented with some bad news. With the Reds leading by three goals to one, Trent Alexander-Arnold picked up an injury concern and had to be substituted for Joe Gomez.

“He told me he got a kick,” said Klopp after the final whistle when asked about his special number 66. “We hope he’ll be okay. Pretty painful. That’s why we changed him.” It remains to be seen whether Alexander-Arnold will recover from his knock against the Cherries, but if there’s one thing that is for sure, it is that he’s never been as integral as he currently is at Anfield.

Since April, the Scouse defender has essentially operated as an architect for the Reds, as he’s been the key to Klopp’s new-look offensive shape. With Liverpool struggling to showcase consistent results and performances in the Premier League at the time, the German coach decided that it was time for a change.

In fact, it was his assistant, Pep Lijnders, who came up with the tactical solution. Every week, Liverpool was relentlessly suffering from counter-attacks on the defensive side of the game, with opponents profiting from the use of quick and direct offensive moves after Klopp’s men had opened up to attack.

Alexander-Arnold was a solution in that sense, as Klopp and Lijnders instructed him to essentially become an inverted full-back rather than one who would hug the touchline on the flanks. The England international started to drift inside whenever his teammates had control of the ball, occupying a spot in central midfield and almost becoming a quarterback of sorts.

The 24-year-old was an extra body in the middle of the park, which helped the team in both attack and defense. It allowed the Reds to govern the middle of the park, while also remaining compact in defense after losing the ball. “If you dominate the midfield, you dominate the game,” said Lijnders on the Training Ground Guru Podcast.

Klopp’s go-to structure was previously 4-3-3 but over the past four months, the 56-year-old coach has favored 3-2-5.

Alexander-Arnold has been the main man behind the shift. When he drifts towards the center circle, many of his teammates proceed to make their own movements. The two number eights in the team push higher up towards the final third, for example, with left-back Andy Robertson tucking inside to become a makeshift wide center-back.

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Everything about Liverpool’s new arrangement is initiated by Alexander-Arnold, and since the shift was enforced earlier this year, the Reds haven’t lost a single competitive match, winning eight and drawing four. The contemporary strategic ploy has restored Klopp’s ability to compete at the summit, but he now has a dilemma on his hands.

Alexander-Arnold has been an ever-present in his team since April, but the knock picked up against Bournemouth could lead him to miss Liverpool’s next match, which looks destined to be a tricky one against Newcastle United. If the academy graduate fails to recover in time, it remains to be seen how Klopp will navigate his void.

Nobody else in his squad has the qualities to do what Alexander-Arnold does. At a push, James Milner had the basic skills to perform as an inverted full-back, but the veteran performer left Anfield this summer and decided to join Brighton and Hove Albion for a new challenge, with Jordan Henderson also departing for Saudi Arabia.

Gomez was the player who replaced Alexander-Arnold against Bournemouth, but the English defender is more of a center-back than a midfielder, and it is reasonable to suggest that he doesn’t have the right profile to operate as an inverted full-back.

Klopp has a void in his squad in that sense, and with the transfer window still open, he could search for a late solution. With a younger number six to go alongside Wataru Endo, the ability to play the inverted full-back role might come into the Liverpool boss’ criteria.

Overall, though, regardless of the options available on the market, Liverpool won’t find anything close to Alexander-Arnold. He is a unique star, and if he’s not on the pitch, Klopp simply cannot play the same way. The Reds defender could be fine to play next week but if he’s not, a new blueprint will be required ahead of his team’s upcoming trip to Tyneside.