The Austrian joined SIPG from West Ham for £23million in July 2019.
As reported by Beanyman Sports, Arnautovic said: "I underestimated it. I didn't train. I didn't look after my body. I was eating. I was drinking fizzy drinks - Sprite, Coca Cola, Fanta - all these sugar drinks that are not good for the body.
"Eating at wrong times. Not sleeping, because when I came to China it took me about three weeks until I could adapt to the time. I went to bed at 6, 7 o'clock in the morning. I woke up 3, 4 o'clock in the afternoon, went to training, stayed up again all night, eating at wrong times.
"This is exactly what I said before. Now I just put in my mind the club wanted me to come, to do well, to play for the title, and I changed because I need to do better and I need to be better. Otherwise you can't play here."