Jürgen Klopp has become the angry young manager of German football. Only a year after Borussia Dortmund were Champions League finalists and two after clinching a second consecutive Bundesliga title his side are a fading force, and Klopp a coach in need of reinvigoration.

Last week the 46-year-old stormed out of the studio of ZDF, a national television channel, when posed a question he deemed beyond the pale.

After Dortmund had gone down 3-0 to Real Madrid in the Champions League quarter-final, the ZDF presenter Jochen Breyer asked if the tie was virtually over. It seemed a reasonable enough question given that even a repeat of last season's 4-1 win over Cristiano Ronaldo and co at the Westfalenstadion, which came at the semi-final stage, would not be enough.

Klopp's reaction belied his urbane reputation. "How can anyone pay my salary if I say the tie is done? I would be just as stupid to say we are going to thrash them but I'm not going to be able to continue standing in this studio to be provoked into saying a stupid thing," he said. "For stupid questions I can give stupid answers."

This prompted Klopp to end the live interview, shake the hand of Oliver Kahn, the former Bayern Munich and Germany goalkeeper who was also present, and ignore Breyer as he stormed out.

"He took the microphone and threw it on the floor and just walked away," says Jan Aage Fjortoft, the former Norway striker who is a German football expert. "So Klopp is not always the charismatic Elvis Presley like you always love to see in press conferences."

This was not the first sight of a disgruntled Klopp on German TV. Previously this season he had taken Kahn to task when the Bayern goalkeeping coach defended the sporting director, Matthias Sammer. In reaction to Sammer's questioning of rival clubs' determination in a championship Bayern romped to, Klopp said: "Let me put it that way; if I was Matthias Sammer I'd thank God every day that somebody had the idea to bring me in. Bayern would not have less points without Matthias Sammer."

In his newspaper column, Kahn responded: "The remark that Sammer does not contribute anything to Bayern was disrespectful and shameless. It is not a coincidence that Bayern's recent dominance started with the arrival of Sammer in 2012."

Later in March, following Dortmund's win over Zenit St Petersburg in the previous round of the Champions League, the pair were in the ZDF studio and debated the Sammer issue, with Klopp just about keeping his cool with Kahn.

The latter's presence once more in the ZDF studio, alongside Breyer last week, hardly helped Klopp's mood. "That was part of the problem," says a highly placed source who reports regularly on Dortmund. "He said to Kahn when he shook his hand before walking out: 'The problem wasn't between us two this time.'

"Klopp's issue is he can't lose. I hear from players that he screams at them in the dressing room. The players who know him for years like him because they know how he is. He's a really great guy when he is winning. The newer players in his squad respect him more than like him. He has to watch out his style of coaching does not alienate the squad."

The spectre of Bayern seems to disturb Klopp more and more. Last summer he lost Mario Götze to "FC Hollywood" and this close season it will be Robert Lewandowski, the Bundesliga's joint top scorer.

This adds to the sense that the clock ticks on a tenure that began in 2008. "Lewandowski will go for free to Bayern and of course that will make Dortmund worse," Fjortoff told TalkSport. "Klopp's linked to Arsenal, he's linked to Manchester United. He has just signed another contract taking him to 2018 but my prediction is that in 2015 [Marco] Reus also has one of those buy-out clauses [that becomes active]. Klopp already lost Götze and Lewandowski. If he loses Reus I think there will be a time where the club will say: 'Well, we don't want this thing any more.'

"And then he can go for an adventure because I don't think he will be the German national coach, [Pep] Guardiola will stay another couple of years at Bayern, so he is one of those who will think this is my chance to go abroad and be a manager."

This campaign's dismal league challenge followed last term's disappointing title defence that ended with Bayern 25 points ahead.

Yet the continent's leading clubs will still fight for Klopp's signature if he were to leave. "Everyone still thinks he's a really great coach – only one of a few who make the team better than the players are," said the source.