Alexander Zverev predicted Jannik Sinner to reach the top of tennis two years ago and it's come true though that wasn't a very hard prediction to make.
Alexander Zverev predicted in November of 2021 that Jannik Sinner will reach the top and it did come true as Sinner broke into the top 10 for the first time about six months after that. It wasn't a very hard prediction to make because Sinner was always considered a top talent with a really good approach so it was mostly about staying healthy and doing the work.
Sinner is yet to properly break out on the biggest stage and win a grand slam but it's likely going to happen sooner rather than later. Zverev's comments in 2021 were:
"I have always thought Jannik would be the youngster to beat soon.. We will welcome Jannik in the top-10 if he gets everything right.. Every time I see him, I feel he has grown more.. I greatly respect Jannik & his game."
They played a couple of times in the psat few years and Zverev usually defeated him.