Doctors later found a bleeding legion on his right vocal cord, which needed to be treated through surgery.
"When someone takes a scalpel to your vocal cord, you think, 'OK, please be careful,'" Donny said. "It's my livelihood, it is who I am. It defines who I am. I am a singer and when that goes away you basically strip me of my identity."
For the operation, Donny put his trust in the expert hands of Harvard Medical School's Dr. Steven M. Zeitels, who has treated singers Sam Smith, Adele and John Mayer.
After the successful surgery, the polyp is now gone and Donny's voice has been restored, but he hasn't had much time to exercise it.
"I just started talking about 10 days ago," Donny told ET. "After the operation, [my doctor] ordered me, no sound -- not even a whisper -- for three weeks. After three weeks, he puts this camera down my throat and I sing for the first time! I put it on my Facebook account, and within minutes millions of people watched it."
Oh Happy Day!I just saw Dr. Zeitels here in Boston. He operated on my vocal chords 3 weeks ago to remove a polyp. ...
Following Donny's recovery, he and Marie's show is coming back to the Flamingo Las Vegas Hotel and Casino on Sept. 29, and Donny even has a new venture that he's unveiling with his wife Debbie -- the Donny Osmond Home collection furnishings.
"It is a major launch," Donny said. "We will have our furniture all over the country."