For far longer than frustrated Liverpool supporters care to remember, it was the buzz phrase that offered hope of success that never materialised.

Each summer, the arrival of a new player was heralded as the last piece of the jigsaw that would transform the Reds from perennial Premier League underachievers to champions of England once again.

It took the arrival of Jurgen Klopp to demonstrate there isn't necessarily one single key to unlocking the championship treasure, although some - such as goalkeeper Alisson Becker, centre-back Virgil van Dijk and forward Mohamed Salah - undoubtedly gave the team a greater shove in the right direction.

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The argument, though, may now have come full circle as Klopp's new-look team, dubbed Liverpool Reloaded by the Reds boss, faces a first serious examination of its capabilities after last weekend's poor 1-1 draw at Luton Town was followed by a surprise 3-2 Europa League group stage defeat at Toulouse on Thursday evening.

With that only a second defeat in 28 games in all competitions - and both setbacks in that time have been laced with VAR controversy - the general curve has been upwards in the last seven months. The uncertainty of much of last season, which in retrospect was partly a hangover from the failed quadruple pursuit of the previous campaign, has long been banished.

Important has been the engine room overhaul that saw more than £150million spent on four midfielders in the summer. Along with the emergence of youngsters such as Jarell Quansah, it has given the squad much-needed fresh faces and reinvigorated the most established squad members.

The nagging suspicion, though, is that something is missing. These are the opening steps of a good Liverpool team, but they cannot become great overnight. And there is one sizeable jigsaw piece that is yet to be put into place - the defensive midfield role.

Certainly, there are no perfect solutions currently available. What many thought was a temporary job for Alexis Mac Allister at the start of the season has become permanent with mixed results, not helped by Wataru Endo's adaptation period surpassing even that of Fabinho back in 2018. And in any case, at 30 years of age Endo cannot be considered one for the long-term.

Curtis Jones and Trent Alexander-Arnold were both used as the number six briefly during pre-season, but neither is best suited to the role, particularly given the positive results that have been engendered by the shift in formation that has released the latter as an inverted right-back and helped the former profit on the left of midfield.

Which leaves injury-hampered Thiago Alcantara, who is out of contract next summer, and teenager Stefan Bajcetic, who is only just starting his senior career. All more than decent, but none ideal for right now.

Of course, Klopp hadn't planned on both Fabinho and Jordan Henderson following James Milner out of the exit in the summer, Liverpool losing in a matter of weeks their three senior defensive midfield options.

The failed pursuits of Moises Caicedo and Romeo Lavia highlighted how the Reds were willing to throw significant money at addressing the matter, while interest in Fluminense's Andre Trindade didn't go beyond an initial inquiry before Liverpool turned to a cheaper option in Endo that subsequently allowed them to swoop for the versatile Ryan Gravenberch on deadline day.

That Liverpool are at present not considering rekindling their interest in Andre - despite the player openly indicating he is ready to leave in the New Year having helped Fluminense win their first Copa Libertadores - suggests there is no appetite to move for a defensive midfielder in January.

More could well be learned about Endo on Sunday when, with Mac Allister suspended and Jones joining Thiago and Bajcetic on the sidelines, the Japan international is likely to make only a second Premier League start for the visit of Brentford.

He could yet prove the answer for the foreseeable. But if such evidence is not forthcoming nearer to January, the voices calling for another final piece of the jigsaw will surely only grow louder. The clock is ticking.