As much as I admire him, it would without a doubt have to be Roger Federer. He is so relentless, attacking every single ball with so much aggression and moving in as soon as he sees the opportunity. He allows no one any recovery time. And by the time you've mustered enough strength to finish one or two sets against him and are physically distraught, he casually walks to his chair and sits down for his drink, looking totally focused yet at the same time disinterested. That would be enough to just make me give up. But that's why he's my favorite player and who I believe to be the GOAT. So, as a tennis player, which pro player (or players) would you dread having to play against the most?