Reilly Opelka is a big fan of Novak Djokovic and how he carries himself off the court believing him to be the GOAT for taking a stand on various issues.
Many tennis players opt to simply go the easy route trying to avoid offending anyone. It's a model that was popularized by Roger Federer and Rafael Nadal whom many consider the perfect tennis players. Neither of them ever created much controversy off the court and that's certainly not the case with Djokovic.
He's always been outspoken about things he thinks are important with the vaccination policies and rules the most recent examples. He stood his ground of 'personal choice' and never got vaccinated despite it having a rather negative impact on his overall legacy. Opelka likes Djokovic for that very reason:
"People like criticizing Novak. He has applied those concepts that he has in life like him having the courage to just take a stand, not play both sides of the coin like how his peers do and just face things head on is the reason why he is the undisputed greatest tennis player that has ever lived."
He also added:
He puts himself on the line and I respect that, part of it because the media has never given him a fair share because like I said, he doesn't play into what they want so he's the enemy of the tennis media. Most players are super grateful for him, he's a pro's pro, he really is."