It's any player's worst nightmare. You work throughout your childhood to make it in the professional game only to see your career ended prematurely by injury. That nightmare became reality for Hansi Flick, Thomas Tuchel and Julian Nagelsmann.

The three Germans will make history this weekthough, becoming the first trio from one country to make the same set of semifinals since the European Cup became the Champions League in 1992-93. They take charge of very different clubs these days, but their successes can be traced back to their formative coaching days in their homeland and back even further to their playing days.

Flick is the senior man, in terms of age, if not top level club coaching experience, and he also had the longest and most illustrious playing career of the three, playing nearly 200 times in the Bundesliga before being forced to hang up his boots at 29. By that stage he'd already won the league four times with Bayern and played in a European Cup final.

When Flick, now 55, was playing in that 1987 loss to Porto, Tuchel (46) was just about to make the step up in to Augsburg's youth team. But he'd never make the grade there, soon departing to find a regular starting spot at regional league side SSV Ulm. Just when he'd started to progress, a knee injury forced retirement at 25. It was even tougher for Nagelsmann, knee problems forced his retirement when he was still in Augsburg's youth setup.

“I felt and thought back then that I wasted all my youth, that it was all for nothing. It just felt terrible," he told Joe.co.uk a couple of years ago.

Starting again

The RB Leipzig boss, now 33, took courses in Business Administration and Sports Science while he struggled to come to terms with the loss of the only thing he'd strived for. But the man he'll meet in Tuesday's first semifinal offered him a way back in to the game. Tuchel was coaching Augsburg's reserve side in 2007-8 and needed someone to scout their opponents, he remembered Nagelsmann's keen footballing brain from their brief time together at the club. "That was my way into coaching," Nagelsmann later said. "I learned a lot from him." 

Tuchel was equally complimentary about Nagelsmann, who he described as "very inquisitive", something that served him well on the Fussball Lehrer (Football Teacher) course run by the German Football Association (DFB), which he completed in 2013. Nagelsmann finished second in his class behind former Schalke coach Domenico Tedesco, who now coaches Spartak Moscow. Tuchel and Flick are also graduates, as is Jürgen Klopp, who reached the last two Champions League finals.

The 10-month course offers emerging coaches the chance to earn the UEFA Pro Licence, the highest coaching badge available in Europe and the minimum requirement for jobs in Germany's top three divisions. But with written and practical exams, mock training sessions, and more than 800 hours of course time (UEFA requires just 240 hours), it's probably the most rigorous test that budding bosses receive anywhere in the world.

While Tuchel and Nagelsmann got their big breaks at Mainz and Hoffenheim after internal promotions from youth coaching roles, another notable feature of the German coaching model, Flick took a road less travelled. After his professional playing career ended, he played for a time with Victoria Bammental in the amatuer game before taking over the coaching role. His time there included a relegation, but he caught the eye of nearby Hoffenheim, who had just started on a journey that would lead from the obscure regional leagues to the Bundesliga and Champions League, largely thanks to the financial backing of Dietmar Hopp.

Learning the trade

A spell working under Giovanni Trapattoni at Red Bull Salzburg proved to be influential in developing defensive systems but it was back within the DFB that Flick began to hone the precise, pressing style that he's now close to perfecting. Flick joined the Germany staff after the home World Cup in 2006 and was at Joachim Löw's side when the country won the trophy in 2014, after which he became the organizations's sporting director. He was in the background but constantly learning. 

That lifelong education has been put to devastating use, with Flick leading Bayern from the doldrums of Niko Kovac's reign to the double and favorites status for the Champions League, with Lyon to come on Wednesday. But it's not just the tactical innovations that have made the difference.

"He is a top human and has a great feeling for us," said Jerome Boateng who, alongside fellow 2014 World Cup winner Thomas Müller, has rediscovered his form under Flick. "Hansi is very respectful and professional with us players, with those who play and those who don’t play. He makes everyone feel that he is important in the team. And that is very important for a club like Bayern."

That understanding with players has also been a key factor for Nagelsmann: "I strongly believe that if you want to be a successful coach, empathy and taking care of the person behind the player is of greater importance than any tactical aspects," he once said.

Relationships matter

Empathy was one of the qualities demonstrated by Tuchel in the most stressful of situations after the bomb attack on Borussia Dortmund's bus in 2017. While that exposed cracks in his relationship with the club's hierarchy that eventually led to his departure, his players spoke highly of his reaction with them. But controlling the egos at a club like PSG is another matter altogether.

The meeting between Red Bull-backed Leipzig and Qatari-owned PSG is not one for the romantics, but the slightly different tactical approaches of the German bosses should make for an engaging contest. Nagelsmann is all about the press and trying to force the opponent in to mistakes high up the pitch.

And, while Tuchel is also an advocate of the style that's come to define modern German football, the particular demands of PSG have meant they've sometimes become over-reliant on their stars, particularly Kylian Mbappe and Neymar, and lacked the sort of cohesion Nagelsmann's sides often display.

Whatever happens there, one of those two Germans will coach in a Champions League final and Flick, who has that unfinished business from his playing days, is pleased to see compatriots at the same stage. 

"I'm naturally happy for Thomas and also for Julian," he said. "I know myself how it feels to reach the semifinals. These are the best club teams, the best clubs in Europe. You're very happy to be there."

While that may be true, none of these three will be satisfied if the story ends there.