The 47-year-old has suffered complications, including blood clots on the lungs, after contracting Covid-19.
“I keep fit, I am active, but this got hold of me very quickly and that was the alarming thing,” Moore said.
“I went downhill rapidly but over the past few days I do feel my body is getting back to where it should be as an individual. That’s a big positive because my body has not been my own.
“By resting I am building my strength and energy levels which will allow my body to strengthen.
“I am chomping at the bit to get back but I have to listen to the medical advice.”
Former West Brom boss Moore left Doncaster Rovers at the start of March to take over at Hillsborough.
But the Owls are in serious danger of being relegated to League One as they are four points adrift of 21st-placed Derby with two games to play.
Moore, who has no set time scale for a return to work, said: “I am gutted, really gutted, because I want to be there. I want to be there at the heart of it, but I have to rest.
“I would like to say a big, big thank you for the unbelievable support I have received. I have been overwhelmed and touched by the love.”
Leicester City star Harvey Barnes has been ruled out for the rest of the season - ending his slim Euro 2020 hopes.
The winger is to have a second operation on his injured knee.
Support The Yorkshire Post and become a subscriber today. Your subscription will help us to continue to bring quality news to the people of Yorkshire. In return, you’ll see fewer ads on site, get free access to our app and receive exclusive members-only offers. Click HERE to subscribe.