Were it not for Paris Saint-Germain coach Thomas Tuchel, Julian Nagelsmann might not now be preparing RB Leipzig for a UEFA Champions League semi-final.

Twelve years ago, Tuchel was coach of Augsburg's reserve team when centre-half Nagelsmann came to the realisation that his injured knee would not sustain a professional career. "After my injury I didn't want to have anything to do with the sport," he told CNN. "I wanted to get away for a while because I had invested so much time in it.

"From one day to another my career was over, faster than I ever imagined."

Watch: Nagelsmann brewing a Bundesliga storm

Tuchel did not let Nagelsmann walk away from the game so easily, though.

"I still had a contract with Augsburg and that's why Thomas approached me and, while he didn't say: 'you're going to be coach', it was more of a pragmatic decision," Nagelsmann told spox.de. "Since Augsburg were still paying me anyway, I started scouting opponents for him.

"Of course I'm very grateful to him for, let's say, giving me the idea of becoming a coach. Thanks to him, I got the opportunity to become assistant to my former youth coach Alexander Schmidt with 1860 Munich's U17s."

From then, things soon spiralled and Nagelsmann's coaching career took off.

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Two years in a coaching capacity in Munich primed Nagelsmann for a switch to Hoffenheim, where he saw his ambitions reciprocated.

"It was definitely a gamble, but I had been shown very early on how good the prospects were of becoming a head coach," Nagelsmann recalled of that move to Hoffenheim's U17s, initially as assistant coach.

It took just 18 months for him to join the first-team coaching staff.

"When [then coach] Frank Kramer called me, I had to laugh," Nagelsmann said. "I didn't think he was being serious. It was definitely weird.

Julian Nagelsmann (r.) was quickly able to convince Hoffenheim players, many of whom were older than him, that he knew more than just how to place cones down on the training field. - imago/Jan Huebner

"I still remember the first meeting with the team. I was pretty nervous when I had Tim Wiese and co. stood around me; all these established professionals. I could tell that they wanted to test me and see if I was just there to put down the cones, or whether I had an idea. They soon realised that I could help them."

It was there that former Germany international goalkeeper Wiese gave Nagelsmann his 'Baby Mourinho' nickname, which has stuck to this day, and after eliminating the Portuguese tactician and his Tottenham Hotspur team in the last 16, it is now Nagelsmann's turn to test Tuchel.

"Games against him are always interesting, because he has a good idea of football," Nagelsmann told Sky after making history by leading Leipzig into the last four. "Hopefully I can also find a decent idea and that the lads play like this again, then we'll have a good match.

Julian Nagelsmann celebrates RB Leipzig reaching the semi-finals of the Champions League, where they will face Paris Saint-Germain. - Peter Schatz/Peter Schatz / Pool

"Of course I was his player, but that was a long time ago. Coaching's my game now, just like it's his."

Coaching has been Nagelsmann's game since Tuchel gave him his break back in 2008, but there is no place for sentiment with a place in the final, and the opportunity to become the next German coach after Jürgen Klopp with Liverpool in 2019 to win the Champions League, up for grabs.

"When you reach the next round, you always want to go further," Nagelsmann said. "That's how a footballing heart beats, and so we want to get to the final, definitely."

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