Zverev said that he has defeated Federer and Djokovic multiple times and has won big tournaments so knows what it takes in a Grand Slam. Despite that he knows that he has to be better physically and mentally to defeat them in these tournaments.
"In the last years I managed to become the world No.3. I defeated Djokovic and Federer several times, in big matches. I also won three Masters 1000s and an ATP Finals.
I know what it takes to beat Federer, Nadal and Djokovic and winning a Grand Slam title against them, the best guys in our sport.
I need to be better physically and mentally and be prepared to potentially beat the three players back to back in a Major. You can achieve it. It's about having a powerful mind and a great physical game. I always said that if we want to win bug titles, we need to compete against those players."
https://twitter.com/AlexZverev/status/1189675652171083776