Magath managed eight clubs in his native Germany over a 17-year period, and whilst there were trophies and cups along the way, he also acquired a certain infamy.
Magath is renowned for his gruelling training sessions, acquiring other monikers such as 'Saddam Hussein' and 'Medicine-ball Magath'.
"I can't say anything negative about him," said Holtby.
"When I was at Schalke, for me it was very important to have him as a manager.
"He built my character and made me grow up very quickly with the hard training, getting mentally and physically right.
"He toughened me up as a person mentally. When you're 18 you grow pretty quickly. That's stayed with me until now.
"I know lots of the press have called him very bad names and I don't think it's right to do that. That's over the line.
"It's a bit of a disgrace if you call someone Saddam. It's not like he killed anyone. He's not a murderer.
"Of course he trains hard, but everyone has his own philosophy. He has his own style of training and you have to respect that, along with the fact he won a couple of titles in Germany.
"As a player it was really hard back in the day. I've witnessed a lot of things. I'm not saying we didn't suffer, but I'm not complaining.
"The thing is you have to graft through it. You have to be happy he makes you fit and mentally very strong."
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