Fangio, 60, was hospitalized on Thursday with a kidney stone, NFL Network's Steve Wyche reported. The team later confirmed the news.
Despite his hospitalization, the Broncos announced that Fangio "is planning on coaching" Thursday night's game.
Fangio arrived at Tom Benson Hall Of Fame Stadium in Canton, Ohio at around 5:50 p.m. ET. The preseason contest kicks off at 8 p.m. ET on NBC.
Denver hired Fangio in January to replace the fired Vance Joseph, who led Denver to a 11-21 record in two seasons.