There have never been any doubts over Rafael Leao's talent.
Former Sporting youth team coach Tiago Fernandes has always maintained that the Almada native "is the best player in the history of the academy".
Better than Paulo Futre. Better than Luis Figo. And, yes, even better than Cristiano Ronaldo at the same age.
The "big problem", as far as Fernandes was concerned, was Leao's "complacency", the feeling that pure talent alone would prove sufficient to propel him to the summit of the game.
It was strange, too, given Leao idolised Ronaldo, a living legend renowned for his incredible work ethic.
"Cristiano is the best in the world," the prodigiously gifted attacker told GOAL in 2018. "He has made a successful career with a lot of hard work and is a great example to follow."
Only Leao didn't. He quickly became as famous for his potential as his lethargy.
Even during his solitary season at Lille, in 2018-19, then-club president Gerard Lopez labelled Leao "The Portuguese Mbappe" but coach Christophe Galtier admitted "He's a player who can make you pull your hair out but, a few minutes later, bring you a lot of hope and a smile."
AC Milan certainly felt Leao was a risk worth taking and paid €23 million (£19m/$26m) for his services in August 2019.
He scored six times during his debut season in Serie A, showing numerous flashes of his awesome ability.
However, Leao was still frustrating fans, coaches and team-mates.Getty/GOAL
Club sources revealed that he sometimes cut a distracted, almost disinterested figure in training.
When Zlatan Ibrahimovic rejoined Milan in January 2020, he immediately took his fellow forward under his wing.
Even Leao soon began referring to the Swedish striking icon as his "big brother".
“Since he arrived, he’s been talking to me, giving me advice on how to improve, how to position myself in the penalty area," the Portuguese explained.
"He’s a great player and I want to learn as much as I can with him by my side."
Ibrahimovic, though, felt that too much of what he was telling Leao was going in one ear, and out the other.
No matter what he said, he couldn't quite seem to get through to Leao, to make him realise just what was expected of a top professional.
Then, during the summer, Leao "totally changed", as Ibrahimovic put it. "He understood himself what to do," the Swede told Corriere TV.
For Leao, the penny had dropped. He couldn't get by just turning it on for 15 minutes here and there. He accepted what Ibrahimovic, Milan coach Stefano Pioli, his parents and his personal trainer were all telling him: he needed to be on it each and every week for 90 minutes.
"God has given me the talent, which is rare, but I must add sacrifices and hard work," he admitted in an interview with La Repubblica in November.
"I have a talent to cultivate but you don't play alone in football and I’ve proved that I can make it at Milan."
He's most certainly done that over the past few months.
Just over halfway through the 2021-22 campaign, Leao has as many goals in all competitions (eight) as he's ever previously managed as a professional over the course of an entire season.
In addition, he's also contributed four assists, has completed more dribbles than any other player based in Serie A (62) and is now set to be rewarded with a bumper new contract.
The upturn in form has also resulted in the Mbappe comparisons resurfacing, but Stefano Pioli feels Leao is more similar to another famous French forward.
"He reminds me a lot of [Thierry] Henry," the Milan coach told reporters earlier this month.
Given Pioli is hardly a man renowned for making outlandish statements, the comparison provoked plenty of debate in Italy.
However, it has been backed up by the likes of Nicola Amoruso and Alessio Tacchinardi, both of whom were on Juventus' books when Henry spent six months in Turin in 1999.
"The young Henry is the Leao of today," Tacchinardi told Tuttosport. "The characteristics of the two players are the same: you see the pace in one-on-ones and they always go on the outside to break through the opponent’s defence.
"I was slaughtered on social media for this comparison. But just compare the videos and there’s nothing else to say: they’re the same."
Amoruso is in total agreement but he added in an interview with the Gazzetta dello Sport: "Leao just has to better understand how strong he is. Once he does this, nobody will stop him."
And this leads us on to the great contradiction in Leao's character.
For all of his faith in his natural talent, he still doesn't seem to have fully grasped just how far he can go.
Italian coaching icon Fabio Capello and Pioli have also said the same thing: Leao doesn't yet realise the enormity of his potential.Getty/GOAL
Still, it's clear from both recent statements, and recent performances, that the player himself has at least started to see the merits of adding industry to innovation.
"I think he has to convince himself and work a lot on his mentality to try to become even more ambitious," added Pioli, whom Leao views as "a reference point" in his career.
"One with his means must think of getting to the top of the world, but talent is not enough. He understands that he has to work in a certain way.”
And work with others.
Encouragingly, Leao now forms one of the most formidable left flanks in Europe alongside Theo Hernandez, with the pair combining to devastating effect to torment opposition right-backs.
Indeed, how Juventus cope with Milan's dual threat out wide will go a long way towards determining the outcome of Sunday's massive Serie A showdown at San Siro.
Leao is clearly not the finished article. He cannot be compared to the Henry that Arsene Wenger transformed into arguably the finest attacking talent the Premier League has ever seen.
Still, there are undeniable similarities to the Henry that toiled in Turin for six months. There is the sensational speed, the devastating dribbling skills and the valuable versatility.
Of course, a key difference is that while Leao is flourishing out wide under Pioli, Henry floundered under Ancelotti.
However, as Tacchinardi pointed out, the Portugal international is another "diamond in the rough", one that could yet be polished into something quite spectacular.
And the signs are that after a couple of seasons of frustration which required an immense amount of patience from Pioli & Co., Milan are finally well placed to succeed with Leao where Juve failed with Henry.