"They didn't explain to me the rules of five sets yet, so somebody needs to tell me I don't necessarily need to play five sets every time I step on the court," Zverev, who has 5-0 match-win record in French Open five-setters, joked after the match.
"I don't think I have ever lost in five sets here. It's a good thing to have in the back of your head. Hopefully I can continue this run."
Fognini has emerged as a French Open dark horse after he lifted his maiden ATP Masters 1000 title in Monte Carlo, beating Rafa Nadal and Zverev in the process.
The ninth seed dismissed Spain's Roberto Bautista Agut in four sets in the third round.
"He's playing very well, hasn't lost more than a set so far in a match," Zverev said.
"It's going to be a difficult match. I'm ready for it. I think I'm playing much better than I have the last few months."
In the day's other key matches, world number one Novak Djokovic will meet Germany's Jan-Lennard Struff, while Juan Martin del Potro takes on Russia's Karen Khachanov in a battle of power-hitters.
(Reporting by Hardik Vyas in Bengaluru; Editing by Toby Davis)
