Pep Guardiola has been slammed in a scathing attack by Bayern Munich's high-profile team doctor, who said the Catalan took the German club "backwards" in some aspects of their training.
In his autobiography, which is being serialised this week in newspaper Bild, Hans-Wilhelm Mueller-Wohlfahrt described current Manchester City boss Guardiola as someone with "low self-esteem who does everything to hide it from others".
"Guardiola is often portrayed in the media as an innovative, if not revolutionary, coach, but at Bayern Munich he turned the clock back," wrote Mueller-Wohlfahrt.
"It even went so far as to turn our medically thought-out, well-rehearsed warm-up programme on it's head before training sessions.
"I think Pep Guardiola is a person of low self-esteem.
"He seems to live in constant fear, not so much of defeat, but much more about any loss of power and authority," Mueller-Wohlfahrt added.
The 75-year-old Munich-based doctor has worked with a host of stars including sprint legend Usain Bolt and Germany's 2014 World Cup winning squad.
Mueller-Wohlfahrt had a stormy relationship with Guardiola, Bayern's head coach from 2013 until May 2016 in which he won three consecutive Bundesliga titles.
The pair fell out in April 2015 when Mueller-Wohlfahrt claims he was verbally attacked by Guardiola after a Champions League defeat in Porto which saw the doctor resign from his Bayern duties.
"While the players were still being treated, I was loudly attacked in front of the assembled team and made responsible for our many injuries," Mueller-Wohlfahrt wrote.
"I was to blame for the physical condition of the players and ultimately for the defeat.
"I felt deeply hurt. I resigned as team doctor of FC Bayern Munich after 38 years."
Mueller-Wohlfahrt, who returned to work with Bayern following Guardiola's departure in 2016, says the Spaniard was "upset every time a player had to come off with a muscle injury."
"After the successful 2012/13 season, then came Pep Guardiola and he knew everything better," said the German.
"Five minutes warm-up in a rush - that had to be enough.
"I simply could not reach Pep Guardiola with the way I think and work.
"Whenever I wanted to talk to him, he immediately turned away and walked away.
"The tensions between us increased over the months.
"Every time I helped a player off, because of a muscle injury, the coach was angry.
"'That's ridiculous, he could continue to play', was what he meant."