Schurrle announced his retirement this year at the age of 29.
"He's a brutal guy," Schurrle told German presenter Joko Winterscheidt. "I always thought to myself: 'What does he do anyway? Why does he treat me like this? Why does he do this to people?'
"In retrospect, I realise what he wanted and what resources he was working with. At the time, I couldn't really deal with the things he wanted from me because of all the harshness and the psychological pressure.
"Back then, it was extremely difficult. I would often drive home after conversations with him and just thought I couldn't do it anymore. What could I do? He was building up such extreme pressure."
The former Germany international conceded his confidence was left in tatters following a series of substitutions from the intense coach.
"It was often the case that I played from the start and then he'd replace me at half time," he added.
"Then, in the next game, I wasn't in the squad and I was in the stands. I couldn't understand that at the time and I lost my self-esteem. My ego was hurt.
"Then I started thinking about what might be going through his mind. Sometimes during training I had the feeling that he was only looking at me, even if that probably wasn't the case."