Japanese player Osaka cited the impact on players' mental wellbeing for her decision, saying the nature of questions from journalists is like "kicking a person when they are down".
After American great Serena Williams, Osaka commands the highest profile of any female tennis player and her decision has left the WTA in an awkward position.
"Of course I'm disappointed not to win it, but at the same time I'm very pleased with the level of tennis that I managed to find in the later stages of this tournament.
"I have to obviously keep the momentum going I feel with the quality of tennis," he said. "Do more training, of course, and few more matches. I think I'm on the right way.
Eighth seed Berrettini, who has dropped only one set in the tournament, will be aiming to win his maiden ATP Masters 1000 title against Zverev on Sunday.
