The former Hamburg and FC Twente star has struggled since his summer arrival.
We gave him a five-year deal which means that his career path with Juventus will be very long," Juve GM Beppe Marotta declared.
"We believe in him and we followed him for some time.
"You can't expect a player to come in from abroad, land in a new environment and get positive results straight away.
"It's clear that he has to find his own way of settling in."