Cael Sanderson said Nagao had "a major surgery" and won't return "anytime soon."
Mesenbrink won his four bouts last week by a combined score of 72-10.
Eighteen out of 22 of the wrestlers placed.
Penn State wrestling's next true freshman starter is poised to make an immediate impact.
Van Ness went 24-7 as a redshirt freshman before a medical redshirt sidelined him last season.
Herring is rated as the No. 20 recruit on MatScouts big board.