"It was over man," the Motown icon told the Daily Mail in an interview. "They had to rush me to the hospital. I got it severely and was hospitalized for 11 days, and four or five of those days, I do not even remember."
The 81-year-old also said he was afraid that the virus had impacted his famously feathery-smooth voice.
"I was not sure that I would ever be able to sing again because it took my voice," he said, adding that he "could barely even talk" while fighting the infection.
"Even when I got home I was hoarse, I could try not to sing because I was afraid," he shared. "It was one of the most frightening fights I have ever had."
The "You've Really Got a Hold On Me" singer attributed his recovery to his high fitness level.
"It sounds weird, I know, but the severity of my condition didn't hit me until it was over," he said. "I looked back and knew I could've died ... It was that severe. Then it scared me."
He said that he's back to his workout schedule and did a lot of work to get his voice back.
"Now I work out almost every day because I don't want to get the virus again, even though I've had both of my shots," the singer said. "I had to work on my vocal cords and get myself back together. I know this was what i wanted to do with my life, and it was possible, so I did it," he added.