(CNN) -- Medical tests show Bret Michaels has suffered a setback in his recovery from a brain hemorrhage, according to a statement posted on his official website Tuesday.
Despite the development, "doctors remain hopeful for a full recovery," the statement said.
The rock singer and reality TV star suffered a massive brain hemorrhage and was hospitalized Friday.
"Doctors state Michaels is very lucky as his condition could have been fatal," it said.
"Test results indicate a setback in Bret Michaels' condition, a side effect from the brain hemorrhage called hyponatremia, a lack of sodium in the body which leads to seizures," said the statement posted by road manager Janna Elias.
Michaels "is responding well to tests and treatments," she said.
"Even though today was a minor setback Doctors remain hopeful for a full recovery and plan to release more specific information next Monday."
Michaels, 47, was the lead singer for the '80s glam-metal "hair band" Poison. He became a reality star on the VH1 show "Rock of Love with Bret Michaels." He has also appeared on "Celebrity Apprentice."
His manager and publicist have been careful not to disclose the hospital or even the city where the singer is being treated. They cite security reasons for the secrecy.
Tuesday's statement offers the greatest detail so far about Michaels' condition and treatment.
"Michaels' medical workup demonstrated findings of a subarachnoid hemorrhage, a type of stroke that causes bleeding in the fluid-filled spaces around the base of the brain," the statement said. "It presents itself suddenly as the sound of a loud gunshot or thunderclap at the back of the head causing severe cranial pain and muscle spasms."
Michaels, who is in critical condition in an intensive care unit, has undergone a continuous series of tests "including angiograms, CT scans, MRIs and transcranial dopplers (TCDs)," the statement said. "With further testing and rehabilitation, they are hopeful that Bret will gradually improve as the blood surrounding the brain dissolves and is reabsorbed into his system, which can be a very painful recovery and take several weeks to months," it said.
The latest statement also addressed possible causes of Michaels' brain hemorrhage.
"Many people are speculating Michaels' head injury suffered from a prop striking the singer at the Tony awards last June is the cause," it said. "Additional studies are planned throughout the week to hopefully detect the exact cause of the rupture."
Michaels, who is a lifelong Type 1 diabetic, had an emergency appendectomy just 11 days before falling ill last week.