Mourinho said then: "Now we want to keep him. We have to wait until he becomes 18 to try to get a permit for him to stay in England.

"It's the rules and we have to accept them. He plays for his national team. Sooner or later the committee has to give him a permit to play in England."

FIFA would not confirm if Traore was one of the 29 players whose signings have resulted in Chelsea being handed a player registration ban for two transfer windows by FIFA's disciplinary committee – a sanction the Blues are contesting.

But his emergence attracted attention and triggered the initial investigation.

Traore officially joined Chelsea on January 1, 2014, signing a four-year deal on the first day of the transfer window opening following his 18th birthday, on September 6, 2013.

He spent his first 18 months as a Chelsea player on loan at Vitesse Arnhem in Holland, with whom the Blues have close links.

Peter Bosz, Vitesse's then boss, said Mourinho was "crazy about him" and wanted Traore to be part of his first-team squad. That came in the summer of 2015.

Suspicion was aroused soon afterwards when a search of the Press Association's picture archive showed Traore playing for Chelsea under-18s, at Arsenal's Emirates Stadium, on October 23, 2011, when he was 16.

FIFA rules prohibit the international transfer of minors aged under 18. Transfers of 16 to 18-year-olds are permitted within the European Union.

It was time to investigate further.

Simple internet searches corroborated Traore's participation in the Arsenal game, with a report on the Gunners' official website listing him in a team alongside Ruben Loftus-Cheek, now a first-team regular.

Further digging revealed Chelsea's interest in Traore was made public when he was just 14, when the Burkina Faso sports minister announced in August 2010 that he would be signing for the Blues.

Traore had impressed at the 2009 Under-17s World Cup, despite his tender age.

He attended the fee-paying Whitgift School in Croydon, south London, but did not play in school competitions.

The school's head of football in January 2016 was former Chelsea player Colin Pates and the school confirmed Traore's attendance.

Those elements prompted further questions, which the Press Association posed to FIFA and also put to Chelsea, initially in October 2015 before publishing a story in January 2016.

Football's world governing body was already dealing with infractions over the recruitment of minors by other clubs, including Real Madrid, Barcelona and Atletico Madrid.

Chelsea were by no means alone and insisted they had done nothing wrong. But this was not just about Traore.

The FIFA regulations over the transfer of minors are clear. There can be no compromise in a safeguarding issue with children.

For every Traore who makes it, there will be countless others who do not. What if they, too, have been displaced from their homes and families? What happens to them next?

Traore is a successful forward in the upper echelons of the European game.

He played for Ajax, on loan from Chelsea, in the May 2017 Europa League final defeat to Mourinho's Manchester United.

Traore joined Lyon for £10million in June 2017, with a reported buy-back option stipulated by Chelsea.

Now 23, he has a place among Europe's elite and played for Lyon in Tuesday's Champions League clash with Barcelona.

His former club are battling to return to a place among Europe's elite and now challenging a transfer ban which has potential long-term repercussions.

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