The 42-year-old singer said Tuesday on Instagram that his illness "has developed into pneumonia."
"Breathing without pain or coughing is difficult & I didn't get much sleep last night, but hopefully the antibiotics do their work and fast," he wrote.
Sligh said in a statement to E! News that he was notified on June 24 that a co-writer had been exposed to COVID-19. Sligh started experiencing symptoms on June 25 and was tested for the virus June 27.
Sligh's wife, Sarah, and his children, Keira, 9, and McCartney, 7, also tested positive for COVID-19 but are recovering. On July 6, Sligh was admitted to the hospital, where he was diagnosed with double pneumonia.
"We're grateful for [the] outpouring of love and prayer form fans and friends and hope that my rough experience reminds people how serious this disease is," he said. "So please, wear masks, social distance and take care of each other."
Sligh is now recovering at home. He said he was feeling better in an update Wednesday on Instagram.
"Thank you for your continued thoughts & prayers," the singer said. "Coughing is still bad but MUCH better than two nights ago."
"Honestly, I just wanna get through this so I can go back to writing & producing songs and artists that I love," he added. "I'm grateful for all of you and your concern."
Sligh will release a new single, "One," on Friday that he hopes "speaks good into our broken country & world."
Sligh was a contestant in American Idol Season 6, which aired in 2007. He is known for the singles "Hero," "Empty Me," "Arise" and "Only You Can Save," and last released the album Sing, Vol. 1 in 2019.