The three-time major champion, coming back from hip surgery, finished his most recent match at 3 a.m. Friday and made a decision to withdraw rather than play again so soon afterward.
The world number three will face Stefanos Tsitsipas for a place in the decider after the Greek upset Belgian third seed David Goffin 6-3 6-4. The top-seeded German is looking to become the first back-to-back victor of the hard-court U.S. Open tuneup since Juan Martin del Potro in 2008 and 2009. "I don't think it's reasonable", Murray said. "(My body) doesn't feel great right now.
"Finishing matches at 3 in the morning is not good", he said, per The Post.
When he did, it handed a walkover into the semi-finals to 19-year-old Australian Alex De Minaur, who ousted 11th seed Steve Johnson and eighth seed Chung Hyeon, both on Thursday.
I don't think I should be put in a position like that. "By the time you finish doing recovery and everything it's 5.30 or 6 o'clock in the morning".More news: Facebook bans Alex Jones' and Infowars pages over violence, hate speech
He will add a third in Washington if he can continue his form at the tournament where his overall record stands at 15-2.
At 21, Zverev was the oldest player in the semifinals along with the 19-year-old Tsitsipas and de Minaur and 20-year-old Rublev. "I'd obviously try and sleep as late as I can, but with the way your body clock is and stuff, you know, you might get a few hours' sleep", Murray said.
Storms earlier in the week forced some men to play twice in one day. "And I'm disappointed with that, because I know that the weather's tricky and I know it is for the scheduling, but it's a very hard position to be in".
Murray had earlier announced he would not be playing in next week's Rogers Cup, which would have been his first Masters tournament since last spring.
On the women's side, two-time Grand Slam victor Svetlana Kuznetsova was to face Kazak eighth seed Yulia Putintseva for a semi-final spot.More news: Higuain Reveals Interest From Premier League Giants
When he got to the sideline after the match concluded, he covered his face with a towel and cried, his chest heaving.
The frustrations included Murray leading the first-set tie-breaker 5-0 only to drop the next seven points and the set.
He is already guaranteed to hit a new career-high ranking inside the top 70 and will bid to reach his first main-tour final.
An emotional Andy Murray sobbed into his towel on the side of the court after a grueling victory over world No. 93 Marius Copil in Washington - a game that finished at 3 a.m. Friday local time.More news: Prosecutors detail how they built Manafort case