The Brain: Why Arsenal want Jurgen Klopp's long-time assistant Zeljko Buvac

Zeljko who? The infamous enquiry which accompanied Wenger upon his arrival at Arsenal could yet be directed at his successor too. Among all the disparate names reported to be a contender to replace Wenger – From Diego Simeone to Carlo Ancelotti and Mikel Arteta – none would provoke anywhere near the level of bemusement as a 56-year-old Bosnian whose last management role came with regional German club Neukirchen in 2001.

Buvac has been at Klopp’s side ever since: first at Mainz, then at Borussia Dortmund and, until this week, at Liverpool too. But the man described as “the brain” by his long-time associate has taken an unexpected break from first-team duties due to unspecified personal reasons and will not be on the touchline for the second leg of the Champions League match against Roma on Wednesday night.

“Zeljko is a master of all forms of training, I learn from him every day,” Klopp once said. But one of football’s most productive partnerships has now been ruptured. With the help of our German office, we profile the man who may now be ready, finally, to come out of Klopp’s shadow.

“As a player, he always knew what the opponent had in mind,” said Ansgar Brinkmann, who played alongside Buvac for two years at Mainz. “He was able to read a game, and if he was in possession he made four perfect decisions out of five. Intuitively, he was a great footballer.”

Still, this attacking midfielder born in 1961 in Omarska, in the former Yugoslavia, only carved out an average playing career. Like Wenger before him, perhaps. During spells with Rot-Weiss Erfurt and Mainz between 1991 and 1995, he never made it out of the 2. Bundesliga. But at the latter club, he forged a relationship which would take him to the very heights of the game.

Just around the corner from Emirates Stadium, a famous pact was made which was to reshape the landscape of British politics for almost two decades. On Upper Street, the affluent thoroughfare which arrows from Angel tube station all the way up to Highbury and Islington, Tony Blair and Gordon Brown met for a fateful meal at a restaurant called Granita in 1994. It was here that their power-sharing agreement was established: Brown would allow Blair a free run in the Labour leadership election with the understanding that his time in the top job would come. Their alliance eventually broke down in spectacular fashion.

At around the very same time in Mainz, two ambitious players came to a slightly different understanding when they were plotting their coaching careers. “We already had an agreement at that time," said Klopp. "Whoever gets a coaching job first, picks the other one as his assistant.” Klopp was still playing at Mainz when Buvac moved into management with Neukirchen in the lower reaches of the German leagues in 1995, but when Klopp landed a prime job at Mainz, then in the 2. Bundesliga, in 2001 he was true to his word. In came Buvac and a partnership of near equals was forged.

With Buvac at his side, Klopp led Mainz to promotion and to Europe, in the 2005-06 UEFA Cup. But it was their time together at Dortmund which saw the “Klopp System”, and Buvac’s part in it, earn global recognition.

When Klopp was approached by Dortmund in 2008, there was never any question that Buvac would not go with him.” Of course I would have liked to keep Buvac as coach,” said Mainz president Harald Strutz. “But it was clear to everyone that Klopp would not be able to do without him at Dortmund. So we understood that.”

Klopp developed an implicit trust with Buvac because they enjoyed such complementary styles. Whereas Klopp is an extrovert, Buvac is an introvert. Klopp exploded on the touchline during matches; Buvac monitored training sessions with a cold, precise eye. The dynamic was established during their playing days at Mainz. “As players they were always the protagonists for me,” said Strutz. “Klopp was the one who roused the team in his own way, and Buvac was the strategist who guided the game.”

It was a yin and yang approach which they applied in coaching too. There was no single boss on the training pitch at Dortmund. “Both take turns to address the players,” Mats Hummels once told SPOX. “Buvac has a lot of tactical ideas that are a big part of our training… If anything goes wrong and we make tactical mistakes, for example, it’s usually him who’s interrupting and explaining how to do it properly.” Peter Krawietz, another integral cog in Klopp’s coaching staff at Mainz, Dortmund and Liverpool, once said of Buvac: “He always has the whole thing in view during all the exercises, just as in our games where he quickly identifies developments and discusses tactical solutions with Jurgen.”

A co-architect of Klopp's distinctive counter-pressing style, the Bosnian is known to obsess over the distances between different components of the team, ensuring that passes are made precisely and powerfully, a defining feature of the Klopp system. Buvac also used to take an active part in training. At pre-season camps with Dortmund, he would instruct players to undertake sprinting drills with the ball for 45 minutes - and join in himself. Putting it succinctly, Klopp once said of the man who helped him to two Bundesliga titles and the 2013 Champions League final with Dortmund: “Zeljko is football expertise made flesh.”

A low-key presence who rarely speaks to the press, Buvac might have a kindred spirit in Arsenal owner “Silent” Stan Kroenke. The Bosnian has always been a reclusive figure, happy doing his work away from the media spotlight. It makes him a complete unknown quantity to the outside world – if not to his colleagues. “We communicate telepathically with each other anyway,” Klopp once said.

Buvac even managed to avoid speaking to the media when Klopp found himself banned from the touchline for a Champions League tie against Marseille in October 2013. Klopp studied the UEFA regulations and managed to relieve his friend of the pressure of talking to the world’s media. Klopp worked out he was able to take the pre-match press conference, “then I have to leave the team before the match… but from 15 minutes after the match I’m allowed to go back to the press conference.”

Buvac broke his silence only once. Speaking to a Dortmund fan publication, he simply said: “I only talk when I have something to say. In our job we do not need two or three people who speak out. Everything else is too much.” But away from the glare of the media, things can change. “Buvac is calm,” Dortmund midfielder Nuri Sahin once said. “Until something goes wrong.”

He still remains an enigmatic figure. But if the reports are true and Arsenal do decide he is the best replacement for Wenger then his life of anonymity, of quietly devising tactical approaches on the training ground to little fanfare, will be over. Buvac will be, against all expectations, one of the most high profile coaches in world football.