"Though we do have medications and treatments aimed at reducing this risk ... they are not always effective and up to 20 percent of patients can have a serious stroke despite our best efforts."
Dr. Carmelo Graffagnino, director of the Duke Neurosciences Critical Care Unit in Durham, N.C., said that aneurysm or not, the initial severity of the bleed is also an important factor.
"The likelihood of further short-term complications depends on how much blood was released during the subarachnoid bleed," Graffagnino said. He said that the fact that Michaels is a diabetic could make his care more complex and increase the likelihood he could experience "complications and slowed recovery."
The latest medical woes for Michaels came just days after an emergency appendectomy he received after falling ill before a concert April 11.
Besides his active performing career, Michaels can be seen each week as a top contender on Donald Trump's NBC reality show "The Celebrity Apprentice," competing against singer Cyndi Lauper and media maven Sharon Osbourne, to name a few of the remaining competitors. He previously starred in VH1's "Rock of Love With Bret Michaels."
ABC News' Sheila Marikar contributed to this report.