"I believe it's just that the guys who are hurt lately, it's mostly because they are 30-plus", the 19-time grand slam champion said.
"Yes, I'm surprised [about Federer's level] but not totally surprised because he's looked after himself at 36 - he never put a lot of pressure on his game physically", the two-time calendar Grand Slam victor added.
Play begins on Day Two of the U.S. open at 11am (4pm BST).
An all-time great, the reigning Wimbledon and Australian Open champion is chasing a 20th Grand Slam title to further extend his lead as the most successful male player throughout history in major competitions.
Rafa Nadal of Spain receives medical treatment on his foot during the men's singles final match against Novak Djokovic of Serbia at the China Open Tennis Tournament in Beijing, China, October 11, 2015. "We never played here in NY, so I think that would be fun for everybody involved".
The women's draw has not been robbed of the same level of star power with the most high-profile withdrawal due to injury being 2011 US Open champion Samantha Stosur (hand).
"I missed it past year".
"I don't think there needs to be that much addressing, because the players, they have the option not to play as much as sometimes they have to or want to", he said.
At 36, Federer isn't likely to play for another eight or nine years but he is playing some of the best tennis of his career at this advanced tennis age - maybe the best tennis.
Canadian Eugenie Bouchard, who is suing the US Tennis Association after suffering concussion in a fall on a locker room floor previous year, plays Russian Evgeniya Rodina on Grandstand.
"Hopefully it will be a night session", he said.
Zverev, the world number six, downed Federer for the Montreal title but slumped first time out in Cincinnati to Tiafoe. "I have enough pressure".
Venus Williams is seeded ninth and fellow American Madison Keys is No. 15. The tournament represents Sharapova's first appearance in a Grand Slam match since the 2016 Australian Open.
Czech Pliskova opens play on Arthur Ashe Stadium at 16:00 BST against Poland's Magda Linette, followed by Germany's Kerber against Naomi Osaka of Japan. Assuming they both win Tuesday, they would both play again on Thursday. "But I think I have a good chance to stay there if I play well these two weeks".
The tournament concludes on September 10.