Cold reality slapped Ndombele in the face. Five other professional clubs had said no, too.
"He was hurt," says Bertansetti.
Something had to change for Ndombele, unfit and unwanted, and that journey home ultimately became a defining moment for the boy who would go on to become the most expensive player in Tottenham history.
The total fee for Ndombele, paid to Lyon in five instalments, could be £63 million. It is an extraordinary show of faith by a club reluctant to spend in recent windows, and few arrivals to the Premier League have generated as much excitement in the past couple of seasons. The spotlight will be on Ndombele early tomorrow, when Tottenham host Aston Villa in their first game of the campaign.
They will be watching at Linas-Montlhery, where visitors will find pictures of a young Ndombele celebrating his youth team triumphs. He was small back then, playing alongside kids almost two years older, and few believed he would ever reach these footballing heights.
It was here where Ndombele first began to sweat out the extra weight after his Amiens rejection. He trained with the club's senior team, which included his older brother Bosso, and ran laps of the pitch with Nordine Baaroun, his former coach who found a personal trainer and sorted Ndombele's diet.
"It was a slow process," says Bertansetti. "It is the nature of his body. He has to work to have this body. His brother is the same. If he does not play sport, he will put on weight. It's genetics."
Baaroun says Ndombele was 6kg overweight. So they worked hard, pumping iron, running, eating well. Despite the lack of interest from leading clubs, Ndombele remained quietly confident.
"He never, never doubted," says Baaroun. "When he came back from Amiens, I asked him: 'Do you think you are going to give up?' He said to me: 'Don't worry, Nordine. I'll go all the way.' He's done what he wanted."
After two months, Baaroun contacted Amiens, asking for a second chance and insisting Ndombele was physically ready to compete. Intrigued by the potential of a leaner, more focused player, they said yes.
"From there, it began," says Baaroun. "He matured suddenly."
The return to Amiens was the first major step towards stardom, then, but the dream started much earlier for Ndombele. He grew up in Epinay-sous-Senart, the middle of three brothers born to parents of Congolese descent. Like so many of the Parisian suburbs, or banlieues, it is an area without wealth. The Ndombeles lived in an eight-storey block known as La Plaine III, and little Tanguy used to dart around the town's marketplace when he was not playing football at the nearby FC d'Epinay Athletico.
As a child, his talent was obvious.
"When he played here, the stand was full of people who had come just to see him," says Novic Bayokila, a childhood friend and former teammate. "He had skill we did not have. It was not a smooth route to get to the top but I always knew he'd make it."
Ndombele's father would serve as the team's "12th man" and his mother worked at a nearby church. Faith has been a constant in Ndombele's life.
"They are a very calm, religious family," says Bayokila.
Those who knew Ndombele then, and those who know him now, speak of an introvert. Despite his spectacular skill as a boy, Ndombele has always been reserved. At times, his timid nature has worked against him.
"People could think he was arrogant," says Bayokila. "He is not the kind of person who would mix with people. He would not go and speak to everybody."
In his home town, there is an affection towards Ndombele and an overwhelming sense of pride at his rise since he left Epinay-sous-Senart.
"We only have football here," says Bayokila. "Football is the escape. When I saw him in the French team, I was almost crying."
From FC d'Epinay Athletico, Ndombele first travelled to Linas-Montlhery at the age of 12. He played with a higher year group and essentially trailed most of his teammates by two years because of his December birthday. In pictures of the squad from the time, Ndombele is dwarfed by some of his friends.
He was good, though, and those physical disadvantages only helped him develop his technical ability.
"That is what made the difference," says Baaroun. "That is why he exploded very late. As soon as he grew up like everyone else, he was better than everyone. I knew he would eventually explode."
Guingamp, in Brittany, liked what they saw of Ndombele, who impressed with his desire to play the ball forward, and signed him to their academy when he was 14. As always, he was one of the more reserved of the young players, exuding an air of nonchalance that was not always appreciated by the coaching staff. He formed a close friendship with James Lea Siliki, who now plays for Rennes.
"We made little mistakes, like everyone," says Lea Siliki. "Sometimes we went to get pizza in secret when we did not finish our meal."
Those late-night carbs and that laid-back attitude did not work in Ndombele's favour when Guingamp and then Amiens rejected him.
"Here we see the incompetence of the clubs," says Baaroun. "The weight is not a handicap. Talent is what is important. The weight should not be a problem. But apparently for professional clubs in France, it is a problem. They want you to bring them a player shaped like Cristiano Ronaldo."
Angers, Auxerre and Caen all turned him down.
"They must regret it, these clubs," says Baaroun.
After his return to Amiens, Ndombele began to develop at a startling rate. He became a first-team regular in 2016, helping the club win promotion to Ligue 1 and earning himself a loan move to Lyon. He made 50 appearances in his first season before signing a permanent deal in 2018.
At Lyon, he impressed with his dynamism and creativity. His dribbling ability, outstanding for a central midfielder, is crucial to his game. Ndombele had the best dribble success rate of any player who completed more than 50 dribbles in Ligue 1 last season. There are plenty of similarities to the departed Mousa Dembele but Ndombele offers far more in the final third of the pitch while also becoming far more conscious of his defensive duties.
There was little surprise when Ndombele received his first France cap last October and Ndombele has surpassed every expectation. As Baaroun says, it has been an "explosion" of talent, and Ndombele has shown no signs of losing momentum.
Tottenham manager Mauricio Pochettino has called for patience: "We need to accept he needs time to adapt to a new culture, a new country, new habits. It is only him who arrived to the club and that makes it more difficult. He is open to improving and learning but needs time [until we] see the best version of him."
It is an understandable approach to take with a player who has arrived to such fanfare. Ndombele, though, has always believed he was destined for this stage. The chubby introvert, sneered at by so many top clubs, has pushed forward to become one of Europe's most exciting midfielders. He will not stop now.
