Dani Carvajal’s first ever appearance in professional football didn’t come in Spain. Instead, it came at the BayArena, 1,080 kilometres away from the Estadio Santiago Bernabéu. With first-team opportunities limited during Jose Mourinho’s spell at Real Madrid, the up-and-coming right-back decided to make a move to Bayer Leverkusen ahead of the 2012/13 season and it was a transfer that changed his life.

Just because there wasn’t going to be much playing time in the Real Madrid first team doesn’t mean that Mourinho didn’t rate Carvajal. It was actually the Portuguese coach who recommended the player to Bayer Leverkusen sporting director Rudi Völler and Real Madrid were confident enough in Carvajal’s potential to include a buy-back clause as part of the €5m transfer. Bayer Leverkusen signed the player on a five-year deal, but Los Blancos could recall him for a reasonable fee during each of the first three summers.

When Carvajal arrived on the banks of the Rhine, he was just 20 years old and he was shy. Simon Rolfes, who was the club captain in 2012/13 spoke to Managing Madrid about Carvajal’s development. “At the beginning, he was coming from Spain as very young player and nobody knew him,” the German explained. “He was training and he was very quiet.”

Yet an end-of-pre-season party saw Carvajal come out of his shell. “We had the training camp at pre-season and then came the last evening where the team goes out and we have a nice evening and there was Dani not so quiet anymore,” Rolfes revealed, smirking. “It was very funny that evening. We were really surprised. We said, ‘okay, who is that guy?’. He was really open and extroverted and it was a really fun evening. Before, we’d thought that he would be the kind of player to sit on the bench, but after this team evening he was another person, also on the pitch. It was really amazing because he then felt comfortable on the team. He must have thought ‘okay, the Germans are not so bad and you can have a nice evening with them’.”

This night of bonding helped the Spaniard on the pitch and he hit the ground running when the Bundesliga season started, from his very first match at home to Freiburg – a 2-0 win. Four of the eight assists he had that season came in his first nine appearances, including the match-winner for Sidney Sam in a 2-1 victory away at Bayern Munich. There weren’t many clean sheets for Carvajal and the Bayer Leverkusen defence that season – just 10 in his 32 appearances – but that was more stylistic than anything else as Sami Hyypiä’s team were all about ambitious and attacking football. “Carvajal perfectly suited to our style of play,” said Völler.

Rolfes, who mostly played just in front of Carvajal in defensive midfield that season, loved the way Carvajal played too. “He played that style that he also plays now at Real Madrid,” Rolfes recalled. “His development went up and up. It was amazing. I liked his style, because he was a very good technical player, but also he has the mentality to win and to fight. At the end of that season, he was top, top, top.”

That wasn’t just the opinion of Rolfes. That was the opinion of several around the league. Users of the Bundesliga’s official website voted him the third-best right-back of the 2012/13 campaign, only behind Philipp Lahm and Atsuto Uchida. Meanwhile, German newspaper Bild had him in their team of the season.

So good was Carvajal that Real Madrid decided to recall him after just one year. “He was very sad, because we bought him but Real Madrid had the chance to buy him back directly,” Rolfes revealed. “They chose to activate the buy-back clause. We had qualified for the Champions League and, at first, he was sad because he wanted to stay here and play the Champions League in the following year with that squad, before then probably going back to Real Madrid. But, he made his way and he was a fantastic player.”

After leaving Spain as a boy, Carvajal returned as a man. “I learned a lot, especially by living alone there, by going to another country, by going to another league,” he said at the time in an interview for the Bundesliga’s website. “I matured a lot as a person. Being young, you acquire a lot of experience and the tactical and physical aspects make you a better player.”

It’s the mix of footballing basics with physicality that Rolfes, who now scours Europe looking for the next Carvajals, believes makes the Bundesliga such a good league for players to develop. Asked why Real Madrid have had so many successful experiences of sending players to Germany, with Jesús Vallejo and Achraf Hakimi two other examples, Rolfes had this to say: “I think it’s because we combine technique and also physical football. Normally the Spanish talents have a very good technique and then they can also develop the physical aspect here. We are not only physical and not only technical in the Bundesliga, it’s a combination. It’s also very professional.”

This is something Carvajal experienced first-hand. His time at the BayArena saw him evolve into a more complete footballer and a more confident person. By the time he returned to Real Madrid, he was ready to go. The following season saw him start at right-back as Los Blancos pursued and secured La Décima. When he had to return to Germany to take on Schalke, Borussia Dortmund and Bayern Munich in the knockout stages, Carvajal knew exactly what to expect. And they knew what to expect of him. They knew he was a player to be feared.