There is an argument put forward by regular followers of Borussia Dortmund that the club’s fortunes took a turn for the worse after the departure of one man, four years ago. It was not a player, nor a manager. It was their fitness coach, Oliver Bartlett.

Bartlett, a London-born Australian, joined Borussia Dortmund alongside Jurgen Klopp on 1 July 2008, having been head-hunted by director Michael Zorc while he was working for the German national team.

He was told to improve the Dortmund players’ athleticism and strength to the point where they could carry out Klopp’s relentless high-pressing game, gegenpressing.

Within the space of three years, Dortmund went on to win the Bundesliga title. They followed that with the League and Cup double in 2012. Significantly, they stayed largely injury-free, the players embracing Klopp’s methods and overpowering opponents with a thrilling, rampant brand of football.

Then, in 2012, Bartlett left to join Austrian club Red Bull Salzburg. Very much a disciple of Klopp, Bartlett was a key figure in implementing a similar pressing game, and Salzburg quickly went on to win the league.

Pep Guardiola, on the receiving end of a 3-0 defeat with Bayern Munich in a friendly in 2013, said: “I have never played in my career against a team that has such high intensity.”

Dortmund, meanwhile, began to struggle with injuries, the list steadily mounting until it came to a head last season as they flirted with relegation, they were in the drop zone during the winter break, before eventually finishing seventh prior to Klopp’s departure.

To say Bartlett’s exit was the reason for Dortmund’s decline is a step too far, but it certainly had a big impact.

Something had changed. Injuries had been mounting for years until, in total, only three Dortmund players came through the last campaign at full fitness, and Klopp’s squad suffered 26 separate muscle injuries. High-profile stars Nuri Sahin, Mats Hummels, Marco Reus, Jakub Blaszczykowski and Ilkay Gundogan were all sidelined as Dortmund flirted with disaster.

The argument, essentially, is that Klopp’s style of high-energy football places too much demand on his players’ bodies until they inevitably break down with a series of niggling muscle injuries, and that without a world-class fitness coach – someone like Bartlett – it is a recipe for disaster.

All of which brings us to Liverpool, and an injury list that threatens to derail Klopp after a promising start at Anfield. After two more injuries in the Capital One Cup win over Stoke on Tuesday, Klopp goes into Friday night’s FA Cup tie at Exeter with no fewer than 10 key players sidelined – six of them with hamstring injuries, including the centre-backs Martin Skrtel and Dejan Lovren, playmaker Philippe Coutinho and - yet again - Daniel Sturridge.

Klopp is facing accusations – most notably from Sunderland manager Sam Allardyce and Reds legend Graeme Souness – that he is burning his players out, wearing them down.

“I don’t think Jurgen has realised how ferocious our league is,” Allardyce said. “These lads are fatiguing now with so many games in such a short period of time and are picking up muscle strains.”

Souness had previously said: "A new manager comes in and all the chat was about high press further up the field. It's hard work to do that for 90 minutes. You can do it in bursts.

"You can do it for an hour, you can do it for 70 minutes, but to do it for 90 minutes is a big demand on your legs. I just think they've fallen foul of that. It's not a coincidence, five hamstrings. To have them all at one time, I think they have to look at what they're doing in training."

Stoke vs Liverpool player ratings Show all 23 1 /23 Stoke vs Liverpool player ratings Stoke vs Liverpool player ratings Jack Butland, Stoke Dealt admirably with a barrage of early long-range shots yet his kicking was questionable. 6/10 Getty Stoke vs Liverpool player ratings Glen Johnson, Stoke Eager to impress against his former club, he was the most willing Stoke player to get forward. 6 Getty Stoke vs Liverpool player ratings Ryan Shawcross, Stoke Typically robust in putting his body on the line at the back, greater composure could have brought his team a leveller at the other end. 7 Getty Stoke vs Liverpool player ratings Philipp Wollscheid, Stoke Liverpool's tempo caused the German problems in playing out from the back. 5 Getty Stoke vs Liverpool player ratings Erik Pieters, Stoke Troubled throughout by the movement of Lallana and Firmino. 5 2016 Liverpool FC Stoke vs Liverpool player ratings Geoff Cameron, Stoke Played after winning appeal against his weekend dismissal, but was sacrificed at half-time after struggling in midfield. 5 2016 Liverpool FC Stoke vs Liverpool player ratings Glenn Whelan, Stoke Failed to deal with Liverpool's high pressing game, but never gave up. 5 Stoke vs Liverpool player ratings Xherdan Shaqiri, Stoke Other than a few neat touches, it was a night to forget for the stylish Swiss forward. 5 Stoke vs Liverpool player ratings Ibrahim Afellay Another who saw little of the ball as the visitors dominated possession high in the Stoke half. 5 2016 Liverpool FC Stoke vs Liverpool player ratings MArko Arnautovic, Stoke A willing runner, but unable to make inroads behind Liverpool's patched up backline. 6 Getty Stoke vs Liverpool player ratings Bojan, Stoke Struggled to make an impact in the match aside from a ten-minute second half spell. 5 Stoke vs Liverpool player ratings Simon Mignolet, Liverpool Little to do, but saved well from Johnson when required. 6 Getty Stoke vs Liverpool player ratings Nathaniel Clyne Liverpool Dealt well with the challenge of Arnautovic down the right flank. 6 2015 Liverpool FC Stoke vs Liverpool player ratings Kolo Toure, Liverpool Liverpool's only fit centre-back stood up to the challenge as Stoke went for height and power in the latter stages. 7 2016 Liverpool FC Stoke vs Liverpool player ratings Dejan Lovren, Liverpool Another to suffer a first half hamstring injury, he had already produced a couple of well-timed challenges. 6 Getty Stoke vs Liverpool player ratings Alberto Moreno, Liverpool Caught out at times in defence, but threatened from an attacking perspective. 6 Stoke vs Liverpool player ratings Emre Can, Liverpool Covered the gap between defence and midfield admirably. 7 2016 Getty Images Stoke vs Liverpool player ratings Lucas, Liverpool Showed experience in midfield, and then made a reliable makeshift defender following Lovren's injury. 8 Stoke vs Liverpool player ratings Joe Allen, Liverpool Mocked after his faux assist for Ibe's winner, but influenced a dominant midfield. 7 Stoke vs Liverpool player ratings Adam Lallana, Liverpool Back in the side, he produced an all-round impressive display that peaked with his run and cross for the winning goal. 8 2016 Getty Images Stoke vs Liverpool player ratings Roberto Firmino, Liverpool Played the lone forward role well, and had linked nicely with his compatriot Coutinho before his removal. 7 Stoke vs Liverpool player ratings Philippe Coutinho, Liverpool Started the night brightly before succumbing to an early muscle injury. 6 2016 Getty Images Stoke vs Liverpool player ratings BEST OF THE BENCH: Jordon Ibe, Liverpool An early replacement for the lively Coutinho, he was his side's biggest attacking threat, scoring the game's only goal. 7 Getty

It is a logical argument, although Allardyce may well be deflecting from his own team's struggles. There have been so many injuries, all of a similar nature in such a short space of time, that it is unlikely to be a case of bad luck. After Liverpool initially seemed to embrace the pressing game, dismantling Manchester City, Chelsea and Southampton, they have visibly run out of steam in recent weeks.

But then again, Klopp is not the first manager to employ a pressing game – Brendan Rodgers did so to such enthralling effect in 2013-14 – and few have suffered such a spate of injuries. The answer instead may be found in the training methods.

So where does Klopp go? He will not abandon the philosophy that brought him so much success in Germany. It is tried and tested. Instead, he may look to bring in a fitness coach, or team, this summer who he feels can condition his players to the strains of gegenpressing. Zeljko Buvac and Peter Krawietz, Klopp’s trusted assistants from Dortmund, are already in place. Could he next make a call to Bartlett? It is surely an obvious choice.