Celtic's Harry Kewell and the Johan Cruyff mantra that fuels his coaching philosophy - Tony Haggerty

It seemed like a throwaway line when new Celtic first-team assistant coach Harry Kewell said it during his first pre-season training session at Lennoxtown on Monday.

It was a statement that should catch the imagination of the support. What it is about Celtic and pre-season training sessions that leave an impression?

Ange Postecoglou did it last year. The 'we never stop' speech to his players in that infamous mic'd up session became a club mantra.

Those three words became a Celtic slogan for our time. They went viral on social media, they became the subject of memes, they ended up emblazoned on T-shirts.

Celtic have a new three-word mantra these days: success never rests.

A Scottish Premiership title triumph and a League Cup win against the odds were impressive but Postecoglou wants more. He wasn't resting on his laurels when he hired Kewell.

The former Leeds United and Liverpool midfielder is going to help him in that quest to make Celtic a stronger force both domestically and where it matters most: on the European stage in the Champions League.

The men from Glasgow's East End are no longer a work in progress; the process is now up and running, established and trusted.

Nonetheless, Celtic are constantly evolving and Kewell was not hired by Postecoglou as some sort of old pals' act. How could he have been? The Aussie duo have never worked together before.

The manager is looking to implement a coaching setup that is always improving and implementing ways to do things better. To help with that he's brought in one of Australia's greatest players. A Champions League winner whose own career was sprinkled with stardust.

Ange Postecoglou won a double in his first season - and wants more

"Harry is someone whom I know through the Australia connection but we have never worked together," Postecoglou said. "He is one of Australia's greatest ever footballers and a guy who has worked really hard to get a coaching career going.

"From afar, the reports that I have had on him are that he will bring some really good qualities in terms of his on-field coaching and his ability to mentor players. It was really important that when the players came back this season they understood that nothing stands still and there is a constant evolution.

"We want to better every year and seeing a couple of new faces on the staff is going to help that. He will bring energy as I know he's super excited about being involved at this level and this football club.

"He's got Champions League experience as a player and has won it. He was an attacking player and that will help the group and the balance we have in the coaching group."

So the message emanating from Postecoglou is precise and crystal clear to Kewell. Put simply: Celtic want to be the best team again this year, only this time they are going to try to do it better.

And, as Kewell says, the hardest thing in football is to play simple.

It was Netherlands, Ajax and Barcelona legend Johan Cruyff who espoused that view first. 

READ MORE: Ange Postecoglou, Jock Stein and Ferenc Puskas - The Celtic throughline that binds football royalty

"Playing football is very simple," he said. "But playing simple football is the hardest thing there is."

Cruyff became known as the father of 'tiki-taka' football and was the Catalan side's most successful coach until being surpassed by his star pupil Pep Guardiola.

Tiki-taka refers to the rapid, precise short passing style that allows the teams which play it to maintain possession for large portions of a match.

Barcelona made 'Tiki-Taka' football look so simple under Cruyff and Guardiola but my goodness they worked ever so hard to perfect it.

Celtic under Postecoglou last season played a style which the Aussie often referred to simply as 'our brand of football'.

What Postecoglou's Hoops play isn't quite tiki-taka but there is certainly a throughline connecting the two styles.

Think of Celtic's rampant first-half display against Rangers in the 3-0 demolition at Parkhead in February. Think of the 48-pass move that led to Hoops midfielder Matt O'Riley's exquisite goal in the 7-0 drubbing against St Johnstone in April.

Kewell has been brought in to improve on that. Let's just pause and reflect on that statement for a moment: can you improve on that?

Postecolgou certainly seems to think so and he sees Kewell as the ideal man who can help him achieve that goal.

Davis Keillor-Dunn played under the 58-cap Australian while he was the first-team manager at Oldham Athletic.

He spoke exclusively to The Celtic Way recently about Kewell's coaching ability on and off the training pitch.

Football legend Johan Cruyff

"He is one of the best coaches I have worked with," Keillor-Dunn said. "As a coach, his attention to detail is second to none. Harry totally prides himself on the work that his players put in on the training pitch. He is non-stop on the training ground and he will not leave until the last player is in the changing room.

"He has a bit of everything and has what it takes to go on and become a top coach. I can really understand why he is going into Celtic as he is the kind of guy who can take the club to the next level in Europe. He knows the level and the standard required to compete at the Champions League level. I just feel he is a perfect fit for the club.

"I'm delighted for Harry that he has got this opportunity at such a big club as Celtic and that he can now showcase his management and coaching skills. I mean no disrespect to Crawley, Notts County, Oldham and Barnet but I think Harry is going to be working with a much higher level of player and that will suit him even more.

"He is used to working with the best. I genuinely believe that Harry can push Celtic on as a club. He is a total perfectionist and he puts in so many hours of training."

Cruyff was a perfectionist too.

If Kewell's soundbite hints that he is indeed somewhat modelling his own philosophy and ideas on that of the football legend then he's certainly going about this coaching business in the right way by joining Celtic and working under Postecoglou.

And if indeed 'success never rests' then it's surely a no-brainer to say that Kewell will improve the current Celtic squad and make them better... or else I'm a Dutchman!