E! presenters Brad Goreski and Nina Parker ended up hosting the event.
"Hey, everyone. As I go into my 20th year on the E! red carpet, I have to say I do not take missing an award show lightly, but unfortunately this year is just so different," Rancic, 46, said in a video statement Sunday.
"As part of E! and NBCUniversal's very strict testing guidelines, especially before an event like this, I did find out that I tested positive for COVID-19. Now as much as I didn't want to hear that, I'm very thankful I heard it before I traveled and possibly could have exposed other people. So, for that, I'm thankful."
Rancic went on to say her husband Bill and their son Duke also tested positive, but everyone is "doing well and taking care each other."
Fox, 56, was also saddened to miss celebrating the stars who created the year's best in television.
"I am terribly sorry I cannot be with my E! family tonight! Unfortunately, I have tested positive for the coronavirus. So, in an abundance of caution, I am isolating myself at home," Fox said in a statement.
"During these unprecedented times, it's more important than ever that we follow all safety and health rules and guidelines to protect ourselves and each other. I'm sending my very best to Nina and Brad, who I know will hold down the fort, and congratulations to all tonight's nominees! I look forward to seeing everyone again soon!"
Jimmy Kimmel is hosting the main Emmy Awards ceremony remotely for ABC because of social distancing practices enacted to slow the spread of the coronavirus.