Looking at the Men's draw, ON PAPER: Nadal does have the toughest quarter out of the Big Three however, the only real threat I can see against Nadal is Khachanov on a potential QF matchup. The other players do not really threat Nadal based on current form.
Cilic and Isner are having a bad year. Even if they reached the 4th round, I do not think they will have the form to really trouble Nadal.
Zverev is just a complete mess right now so yeah...
Thiem is a big question mark because it is still a hard court and we do not really know which version of Thiem really shows up in this tournament. In addition, if he does reach the semifinals will he be fresh or tired? It is why I has happy that Federer landed on Djokovic's half.
Even though Millman defeated Federer last year here, I do not think Millman can repeat the same performance against Nadal this year. Besides, Nadal will be ready for the milkman.