Pointing to the quality of the Italian league, he has explained that he is confident Ronaldo will remain at Real Madrid.
"I think that Cristiano Ronaldo will stay," he told La Gazzetta dello Sport. "He plays at the best club in the world and has won everything there.
"I don't see why he'd have to go to Juventus.
"The Italian league isn't at the same level as in the past.
"There are signs that it's improving and their teams have done well in the Champions League and Europa League in recent seasons, but they still haven't reached the level of the Spanish or English clubs."
Furthermore, the German believes that Ronaldo might struggle with the defensive style of Italian football.
"The Italian style of play isn't for Ronaldo," he said.
"All of the players will be watching him.
"The play is more defensive and he'd lose speed.
"What he'll never lose, though, is his motivation, as he is a unique professional."