Back in 2006, when a teenage left-back called Marcelo made a huge impression with Fluminense in his home city of Rio de Janeiro, a consensus was already forming: this was a player whose long-term future was likely to be in midfield.
Thirteen years later, the consensus remains.
Many believe that he is still destined to feature in midfield. It will surely take place one day, but Marcelo is already 30; he has spent more than a decade as Real Madrid's left-back. Whatever happens in the future, he is likely to be remembered as an attacking left-back. And yet the question still hangs over him: is left-back really his best position?
It seems bizarre that any doubts should still remain. After all, Marcelo has been an important member of a side that have won the Champions League and the Club World Cup four times, including in each of the past three years. But it could be that the question will be especially pertinent, both for club and country, in 2019.
Marcelo has proved a worthy successor to his compatriot -- the great Roberto Carlos -- as Real Madrid's left-back, but there is a difference. Both were wonderful going forward -- Marcelo has more subtlety in his attacking game, whereas Roberto Carlos had the edge in terms of explosive power -- but in defensive terms, it is no contest.
True, there were times when Roberto Carlos was caught upfield, but that was primarily a problem for the coach, who needed to find a way to balance out the side and cover the attacking breaks of his left-back. But when Roberto Carlos was back in position, he was a formidable defensive force. The same is not true of Marcelo. There has always been a vulnerability about his defensive play. The recent Club World Cup made this very clear. Free to push forward against Kashima Antlers and Al Ain, he was a splendid sight. But Kashima's goal featured a characteristic piece of loose marking, and he very nearly gifted Al Ain the lead with a disastrous back header.
With Real Madrid in a phase of transition, the weakness of the left side of their defence has been frequently exposed in the first half of the season, with pundits referring to the "Marcelo Avenue." This is the route that Ajax will surely try to take as they seek to end Real's recent domination of the Champions League. As 2018-19 enters the business end, Marcelo's ability to defend will certainly come under the spotlight at Real Madrid -- and the same is true with his international career.
Despite scoring a memorable goal on his Brazil debut -- against Wales just after the 2006 World Cup -- Marcelo has had a mixed time with the national team. He fell out with coach Dunga and missed the 2010 World Cup, he was one of the worst members of the team that fell apart in that extraordinary 7-1 defeat to Germany in the 2014 semifinal, and the left side of the Brazil defence was exposed by Belgium in last year's 2-1 quarterfinal elimination.
Brazil coach Tite accepts that the balance of the midfield was not correct in Russia. He wants to persist with the idea of Philippe Coutinho in the midfield trio, and concedes that the only way to make this viable is to have his full-backs adopt a more cautious approach.
He is not looking for his full-backs to fly up the flanks like auxiliary wingers. Instead, he wants them to tuck in as auxiliary midfielders, forming part of the defensive block while also creating from deep. This means that he does not want the Marcelo of Real Madrid, he wants a different type of Marcelo -- similarly constructive but less adventurous. Can it be done? Can he set up the play while keeping -- or acquiring -- more defensive discipline?
So far, Marcelo has yet to appear for Brazil since the World Cup. This, though, is a coincidence. He was left out of the squad for September's matches, but recalled for both October and November. Both times, though, he had to pull out injured. Tite is still counting on him for this year's Copa America.
There are still plenty of challenges for Marcelo the left-back before he makes the switch to midfield.