Pogba is preparing an appeal after he was banned for four years after failing a drug test at the start of the season.
Marchisio, who played with Pogba in his first stint with Juve, told AS: "Everything he is experiencing hurts me a lot, between physical and personal problems and the issue of doping.
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"He was one of the teammates who impressed me the most on the field, injuries did not allow him to have the career he deserved, he could have aimed for the Ballon d'Or.
"I think it was a mistake to return to United, his evolution did not help."
Marchisio has just launched his player agency company, 'Circum'.
He said: "Everyone must find their vocation. I didn't want to be a coach because in recent years I have focused on the individual rather than the team and my character led me here. Those who appreciate me, know my way of being. I won't change in this role."