The filmmaker said he was admitted into the intensive care unit last weekend. He had been busy promoting his forthcoming project, "Where to Invade Next," described on the film's website as a comedy in which Moore "confronts the most pressing issues facing America today and finds solutions in the most unlikely places."
On Friday, Moore asked his fans for help promoting the film, which hit theaters February 12.
"I have to be honest, with my absence this week (and probably into next), I'm now worried about my film's release," he wrote on Facebook. "I can't fly, I have to recover, and in one week (February 12th) this great movie I've put so much of my life into is going to open in theaters -- with little or no assistance from me."
Moore, 61, asked his fans to "pitch in where you live (and on [social] media) to let people know about my movie."
"I know this seems a bit unorthodox, and I've never seen a request like this made before by a director," he continued. "But this is the age of social media and we're all trying lots of new ways to do things, aren't we?"
It's unclear if Moore, who said he was to be discharged Friday, has left the hospital.