Parts of the Liverpool team sheet are often easy to fill in.
Mohamed Salah, Sadio Mane and Roberto Firmino are clearly the main men in attack.
Likewise, Alisson and Virgil van Dijk take their places at the heart of the defence.
The Dutchman’s partner at centre-back has chopped and changed a fair bit as injuries have struck in recent seasons.
But Joe Gomez is the face you would usually expect to see there alongside him.
Trent Alexander-Arnold is a near permanent fixture on the right side of the pitch.
Midfield is something of a different story, with a blend of talents allowing Jurgen Klopp to tweak personnel and approach depending on the opponent.
But what about left-back?
Up until this week, the answer could not have been more obvious.
He is among the very best in the world in his position and is a vital element in Klopp’s winning machine.
However, the signing of Kostas Tsimikas from Olympiacos for £11.75m arguably represents a new element to transfer strategy under FSG in the Klopp era.
This may be the first time in recent seasons that Liverpool have signed a player to provide direct competition to a more established star.
A case can be made, perhaps, for the arrival of Fabinho.
It laid down the gauntlet to Jordan Henderson who had mostly been occupying the deeper midfield berth.
But the skipper had previously played further forward and has thrived there again since.
The Brazilian provided a new specialist solution which in turn unlocked a dimension that was already present in Henderson’s game.
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Liverpool’s dressing room has boasted several capable understudies for quite a while.
Divock Origi and Xherdan Shaqiri have proven they can fill in when required up front. Takumi Minamino will be hoping for more opportunities to show his skills too.
Neco Williams could be next in line at right-back, while Harvey Elliott looks a fine wide forward in the making.
But are any of them currently expected to put fulsome pressure on a first-teamer?
Early indications suggest Tsimikas is certainly ready to give that a try.
The Greek international was rightly generous with his praise when he discussed the notion of competing with Robertson.
Yet he did not shy away from embracing the challenge.
Tsimikas said: “He’s (Robertson) one of the very good talents. For me, I will give my best to play.
“I know Robertson is one of the best left-backs in the world but this gives me extra motivation to work hard.”
Klopp’s comments expressed a similar sentiment.
The boss said: “[Tsimikas] is a very good footballer with an attitude to win and to compete, and I really like his mentality. It fits perfectly with the mood and the desire we have in our dressing room already.
“Kostas knows from personal experience what is required to challenge and succeed domestically and in the Champions League, and he is ambitious for more – just like us.
“He has come up against some very tough opponents in the past couple of seasons and done well and we know he relishes the challenge, which is perfect for us.
“For that reason we are delighted to know we’ll have him with us for the years ahead. I’m so pleased.”
Tsimikas is 24 with plenty of experience of domestic and European action.
The step up to play for the Premier League champions will be tough. Just like Robertson, it may take him a while to adapt.
But all the signs are that he possesses the ability to offer another option down the left.
He is a talent Liverpool have been watching closely for three years, monitoring subtle improvements in his play and sealing a deal when the time was right.
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And Klopp has never been one for collecting footballers who will not get minutes on the pitch.
Just last month the German said: “Squad building is pretty tricky. It is a big challenge every year. But the answer is never to have more players than you need.
“Actually, that is not the answer! It feels comfortable for a moment but then over the whole year you have different problems.
“That’s why it’s difficult to decide the right number or the right alternatives, but that’s the job to do. So far we’ve done okay, hopefully it will stay like this.”
It could turn out that the recruitment of Tsimikas is another exercise in marginal gains.
He may simply provide left-footed cover for Robertson and allow the gifted Scot to take the occasional well-earned rest.
But there is also the tantalising prospect of a genuine alternative who will freshen up the dressing room and help raise the soaring standards even further.
More direct competition may be a necessary step to squeeze more improvement out of this exceptional squad and take the team to the next level.
Liverpool will surely be the beneficiaries whichever way it works out. Let battle commence.
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