Former Manchester United boss Sir Alex Ferguson has undergone emergency surgery after suffering a brain haemorrhage.
Here we look at what causes the condition, how it is treated and the prognosis for the future.
What is a brain haemorrhage?
Put simply, a brain haemorrhage is bleeding in or around the brain. It causes swelling, and the pooled blood forms a mass known as a haematoma, increasing the pressure on the brain and reducing vital blood flow.
People who experience the condition will sometimes develop symptoms similar to a stroke, with weakness on one side of the body or a feeling of numbness. Sometimes patients will experience a severe headache or difficulty speaking or seeing.
What causes bleeding on the brain?
There are a number of reasons why brain haemorrhages can occur.
According to Luke Griggs, of the brain injury charity Headway, the condition can sometimes happen spontaneously as a result of a ruptured aneurysm, otherwise known as a haemorrhagic stroke.
"A haemorrhage can also result from a blow to the head," he added, "often of a significant severity. But it can sometimes occur after a seemingly minor head injury.
"It can be extremely serious and require urgent medical intervention."
Other causes can include high blood pressure, leading to weakening arterial walls and causing them to rupture, or weakened blood vessels.
What is involved in the surgery and how does it help?
In some cases of brain haemorrhage, an operation is needed to relieve the pressure on the brain. Draining the haematoma will reduce the size of the pooled blood, while surgeons can also repair damaged blood vessels.
There are several ways a surgeon can drain the pooled blood, including by removing a portion of the skull or drilling a small hole in it.
The decision to operate will depend on a range of factors, including the location of the haemorrhage.
A bleed on the brain can also be treated through medication to reduce the swelling.
What is the outlook for patients?
The outlook can vary depending on many factors, including where the bleed occurred and the size of it.
Mr Griggs said: "Every brain injury is unique, as is every individual's recovery."
Many patients will survive a bleed on the brain, but recovery can take many months. In some cases, extensive rehabilitation is needed to regain function, including speech therapy and physical therapy.
Some people can be left with persistent weakness or residual seizures, headaches or memory problems.